[Tex/LaTex] How to add vertical lines at the extreme left and right of a poster using beamer

Question

How can I add vertical lines at the extreme left and right of a poster (using beamer) so that it is wholly surrounded by a box ?

For the moment, my poster looks like that

http://www.docdroid.net/wdte/test.pdf.html

that is, I have two horizontal lines at the top and at the bottom and I want to add two vertical ones to close the box. I am using the beamer theme named I6pd2.

Shown are my minimal .tex document

\documentclass[final]{beamer}
%\usepackage{grffile}
\usepackage[framemethod=default]{mdframed}
\usepackage{showexpl}
\usetheme{I6pd2}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{psfrag}
\usepackage{amsmath,amsthm, amssymb, latexsym}
%\usepackage{times}\usefonttheme{professionalfonts}  % obsolete
\usefonttheme{serif}
\graphicspath{ {./img/} }
%\boldmath
\usepackage[orientation=portrait,size=a0,scale=1.4]{beamerposter}
% change list indention level
% \setdefaultleftmargin{3em}{}{}{}{}{}
\usepackage{tikz}
\providecommand\thispdfpagelabel[1]{}
%\usepackage{snapshot} % will write a .dep file with all dependencies, allows for easy bundling
\usepackage{pgfplots}
\usepackage{ragged2e}

\usepackage{array,booktabs,tabularx}
\newcolumntype{Z}{>{\centering\arraybackslash}X} % centered tabularx columns
\newcommand{\pphantom}{\textcolor{ta3aluminium}} % phantom introduces a vertical space in p formatted table columns??!!
\newcommand{\psihat}{\hat{\psi}}
\newcommand{\phihat}{\hat{\phi}}
\newcommand{\rt}{(\mathbf{r},t)}
\newcommand{\xt}{(x,t)}
\newcommand{\ket}[1]{\ensuremath{|#1\rangle}\xspace}
\newcommand{\bra}[1]{\ensuremath{\langle #1|}\xspace}
\newcommand{\elemm}[3]{\ensuremath{\bra{#1}#2\ket{#3}}\xspace}
\newcommand{\braket}[2]{\ensuremath{\langle #1|#2\rangle}\xspace}
\newcommand\psfragg[2]{\psfrag{#1}{\small #2}}
\definecolor{darkgreen}{RGB}{0,100,0}
\definecolor{darkred}{RGB}{100,0,0}
\definecolor{darkblue}{RGB}{75,25,100}

\listfiles
\definecolor{darkgreen}{RGB}{0,100,0}
\newcommand{\myref}[5]{\textcolor{darkgreen}{{\footnotesize [#1 \textit{et al.} #2 \textbf{#3}, #4 (#5)]}}}
\newcommand{\myrefarxiv}[1]{\textcolor{darkgreen}{{\footnotesize [arXiv #1]}}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\title{A}
\author{B}
\institute[C]{D}
\date{}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newlength{\columnheight}
\setlength{\columnheight}{105cm}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\begin{frame}
\begin{columns}
% ---------------------------------------------------------%
% Set up a column 
\begin{column}{.33\textwidth}
\begin{beamercolorbox}[center,wd=\textwidth]{postercolumn}
\begin{minipage}[T]{.98\textwidth}
\parbox[t][\columnheight]{\textwidth}{
% ---------------------------------------------------------%
% fill each column with content            
\begin{block}{}

\end{block}

\begin{block}{}            

\end{block}

\begin{block}{}      

\end{block}
\vspace{1cm}
\begin{mdframed}[style=innerleftmargin=20pt,innerrightmargin=20pt, innertopmargin=0pt, skipabove=0pt,skipbelow=0pt, linewidth=2pt]%
\usebeamerfont{block body}%
\begin{beamercolorbox}[leftskip=1em,colsep*=.0ex,sep=0.5ex,vmode]{block body}%

\end{beamercolorbox}
\end{mdframed}%
}

\end{minipage}
\end{beamercolorbox}
\end{column}
% ---------------------------------------------------------%
% end the column
% ---------------------------------------------------------%
% Set up a column 
\begin{column}{.33\textwidth}
\begin{beamercolorbox}[center,wd=\textwidth]{postercolumn}
\begin{minipage}[T]{.98\textwidth} 
\parbox[t][\columnheight]{\textwidth}{ 
% ---------------------------------------------------------%
% fill each column with content

\begin{block}{}

\end{block}

\begin{block}{}

\end{block}
\vfill
}
% ---------------------------------------------------------%
% end the column
\end{minipage}
\end{beamercolorbox}
\end{column}
% ---------------------------------------------------------% 

% ---------------------------------------------------------%
% Set up a column 
\begin{column}{.33\textwidth}
\begin{beamercolorbox}[center,wd=\textwidth]{postercolumn}
\begin{minipage}[T]{.98\textwidth} 
\parbox[t][\columnheight]{\textwidth}{ 
% ---------------------------------------------------------%
 % fill each column with content

\begin{block}{}

\end{block}

\begin{block}{}

\end{block}
}
% ---------------------------------------------------------%
 % end the column
\end{minipage}
\end{beamercolorbox}
\end{column}
% ---------------------------------------------------------% 
\end{columns}
\end{frame}
\end{document}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Local Variables: 
%%% mode: latex
%%% TeX-PDF-mode: t
%%% End:

and the corresponding theme

\ProvidesPackage{beamerthemeI6pd2}  % this style was created by Thomas Deselaers an Philippe Dreuw

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\RequirePackage{tangocolors}
\selectcolormodel{cmyk}
%\mode<presentation>

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\setbeamercolor{headline}{fg=black,bg=myblue1} % Cadre du dessus et du dessous
\setbeamercolor{footline}{fg=tabutter, bg=ta3gray}
\setbeamerfont{footline}{size=\large,series=\tt}
\setbeamercolor{separation line}{bg=myblue3} % Ligne de séparation entre poster et cadre du dessus et du dessous
\setbeamercolor{title in headline}{fg=myblue3} % Couleur titre
\setbeamercolor{author in headline}{fg=black} % Couleur auteurs
\setbeamercolor{institute in headline}{fg=black} % Couleur instistut

\setbeamercolor{framesubtitle}{fg=ta3orange, bg=ta2gray} 
\setbeamercolor{author in head/foot}{fg=ta2orange, bg=black}
\setbeamercolor{title in head/foot}{fg=ta2orange, bg=black}

\setbeamercolor*{normal text}{fg=tachameleon, bg=myblue1} % Couleur du fond du poster
\setbeamercolor*{block body}{bg=white,fg=black} % Couleur du texte et du fond des cadres
\setbeamercolor*{block title}{fg=black,bg=myblue2} % Couleur titre cadre
\setbeamerfont{block title}{size=\large,series=\bfseries}
\setbeamercolor{upper separation line head}{fg=ta2orange}

\setbeamercolor*{example body}{fg=ta3aluminium,bg=black}
\setbeamercolor*{example text}{fg=ta3aluminium,bg=black}
\setbeamercolor*{example title}{bg=taorange,fg=ta2gray}

%\setbeamercolor{alerted text}{fg=ta3gray}

%\setbeamercolor{example text}{fg=taorange}
\setbeamercolor{structure}{fg=myblue3} % Couleur des items

\setbeamertemplate{itemize items}[triangle]
\setbeamertemplate{navigation symbols}{}  % no navigation on a poster

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mdfdefinestyle{topbox}{bottomline=false,innerleftmargin=0pt,innerrightmargin=0pt, innertopmargin=0pt, skipabove=0pt,skipbelow=0pt, linewidth=2pt}
\mdfdefinestyle{bottombox}{topline=false,innerleftmargin=20pt,innerrightmargin=20pt, innertopmargin=0pt, skipabove=0pt,skipbelow=0pt, linewidth=2pt}
\setbeamertemplate{block begin}{
  \vskip.75ex
\begin{mdframed}[style=topbox]%
  \begin{beamercolorbox}[sep=0pt, ht=4ex,dp=0.5ex,center,colsep*=0ex]{block title}%
    \usebeamerfont*{block title}%
    \vbox to 3ex{{\vfil\insertblocktitle\vfil}}% phantom because of baseline problem
  \end{beamercolorbox}%
\end{mdframed}%
\begin{mdframed}[style=bottombox]%
  {\ifbeamercolorempty[bg]{block body}{}{\nointerlineskip\vskip-0.5pt}}%
  \usebeamerfont{block body}%
  \begin{beamercolorbox}[leftskip=1em,colsep*=.0ex,sep=0.5ex,vmode]{block body}%
    \ifbeamercolorempty[bg]{block body}{\vskip-.25ex}{\vskip-.75ex}\vbox{} \justifying %
}

  \setbeamertemplate{block end}{
  \end{beamercolorbox}
\end{mdframed}%
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mdfdefinestyle{topbox}{bottomline=false,innerleftmargin=0pt,innerrightmargin=0pt, innertopmargin=0pt, skipabove=0pt,skipbelow=0pt, linewidth=2pt}
\mdfdefinestyle{bottombox}{topline=false,innerleftmargin=20pt,innerrightmargin=20pt, innertopmargin=0pt, skipabove=0pt,skipbelow=0pt, linewidth=2pt}
\setbeamertemplate{exampleblock begin}{
  \vskip.75ex
\begin{mdframed}[style=topbox]%
  \begin{beamercolorbox}[sep=0pt, ht=4ex,dp=0.5ex,center,colsep*=0ex]{block title}%
    \usebeamerfont*{block title}%
    \vbox to 3ex{{\vfil\insertblocktitle\vfil}}% phantom because of baseline problem
  \end{beamercolorbox}%
\end{mdframed}%
\begin{mdframed}[style=bottombox]%
  {\ifbeamercolorempty[bg]{block body}{}{\nointerlineskip\vskip-0.5pt}}%
  \usebeamerfont{block body}%
  \begin{beamercolorbox}[leftskip=1em,colsep*=.0ex,sep=0.5ex,vmode]{block body}%
    \ifbeamercolorempty[bg]{block body}{\vskip-.25ex}{\vskip-.75ex}\vbox{} \justifying %
}

  \setbeamertemplate{exampleblock end}{
  \end{beamercolorbox}
\end{mdframed}%
}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setbeamertemplate{headline}{  
  \leavevmode
 \begin{beamercolorbox}[wd=\paperwidth]{upper separation line head}
    \rule{0pt}{3pt}
  \end{beamercolorbox}
  \begin{beamercolorbox}[wd=\paperwidth]{headline}
    \begin{columns}[T]
      \begin{column}{.02\paperwidth}
      \end{column}
      \begin{column}{.80\paperwidth}
        \centering
        \vskip10ex
        \usebeamercolor{title in headline}{\color{fg}\textbf{\LARGE{\inserttitle}}\\[1ex]}
        \vskip7.5ex
        \usebeamercolor{author in headline}{\color{fg}\Large{\insertauthor}\\[2ex]}
        \usebeamercolor{institute in headline}{\color{fg}\large{\insertinstitute}\\[1ex]}     
      \end{column}
      \begin{column}{.15\paperwidth}
        \vskip8ex
        \begin{center}

        \end{center}
        \vskip2ex
      \end{column}
      \begin{column}{.02\paperwidth}
      \end{column}
    \end{columns}
    \vskip2ex
  \end{beamercolorbox}

  \begin{beamercolorbox}[wd=\paperwidth]{lower separation line head}
    \rule{0pt}{3pt}
  \end{beamercolorbox}
}

%  \setbeamertemplate{headline}{  
%    \leavevmode
%    \begin{beamercolorbox}[sep=0.5cm,wd=.8\paperwidth]{headline}
%      \usebeamercolor{title in headline}{\raggedleft\color{fg}\textbf{\LARGE{\inserttitle}}\\[1ex]}
%      \usebeamercolor{author in headline}{\raggedleft\color{fg}\large{\insertauthor}\\[1ex]}
%      \usebeamercolor{institute in headline}{\raggedleft\color{fg}\large{\insertinstitute}\\[1ex]}     
%    \end{beamercolorbox}%
%    \begin{beamercolorbox}[wd=.2\paperwidth]{logo in headline}
%      \centering
%      \LARGE{LOGO}
%    \end{beamercolorbox}  


%}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setbeamertemplate{footline}{
  \begin{beamercolorbox}[wd=\paperwidth]{upper separation line foot}
    \rule{0pt}{3pt}
  \end{beamercolorbox}

  \leavevmode%
  \begin{beamercolorbox}[ht=4ex,leftskip=1em,rightskip=1em]{headline}%
    \textcolor{black}{\texttt{xxx}}
    \hfill
    \textcolor{black}{\texttt{yyy}}
    \vskip1ex
  \end{beamercolorbox}
  \vskip0pt%
  \begin{beamercolorbox}[wd=\paperwidth]{lower separation line foot}
    \rule{0pt}{3pt}
  \end{beamercolorbox}
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Display a grid to help align images ... and it looks nice with this color scheme
%\beamertemplategridbackground[1cm]

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\mode<all>

% adapt height of imtemize rectangles
\setbeamertemplate{itemize items}[circle]
\setbeamertemplate{itemize item}{\raisebox{0.12ex}{$\bullet$}\hskip0.1em}
\setbeamertemplate{itemize subitem}{\raisebox{0.12ex}{$\circ$}\hskip0.1em}
% or define your own template using \defbeamertemplate{itemize item}, see beameruserguide.pdf

% equal font sizes for all levels
\setbeamerfont{itemize/enumerate body}{size=\normalsize}
\setbeamerfont{itemize/enumerate subbody}{size=\normalsize}
\setbeamerfont{itemize/enumerate subsubbody}{size=\normalsize}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Local Variables: 
%%% mode: latex
%%% TeX-PDF-mode: t
%%% TeX-master: "poster-surf"
%%% End:

Answer 1

You are already using TiKZ, then you can use

\tikz[remember picture,overlay]{\draw[red, line width=1cm]% 
     ([shift={(1cm,-1cm)}]current page.north west) rectangle%
     ([shift={(-1cm,1cm)}]current page.south east);}

to draw a rectangle around the poster. Of course you need to adjust line width, color and corners (shift) according your taste.

My first idea was just include previous command inside poster frame, but How does beamer build the frame? shows that footline is the last layer to be drawn and this is done inside \end{frame}. Therefore, anything you draw inside a \frame can be overdrawn by footline contents.

A solution for this problem could be to include previous TiKZ command inside footline template definition as following code shows. (Note: I've simplified the example and used original I6pd2 theme)

\documentclass[final]{beamer}
\usetheme{I6pd2}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usefonttheme{serif}
\usepackage[orientation=portrait,size=a0,scale=1.4]{beamerposter}
\usepackage{tikz}
\providecommand\thispdfpagelabel[1]{}
\definecolor{darkgreen}{RGB}{0,100,0}
\definecolor{darkred}{RGB}{100,0,0}
\definecolor{darkblue}{RGB}{75,25,100}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\title{My poster}
\author{Me}
\institute[My institute]{A longer name for my institute}
\date{}

\setbeamertemplate{footline}{
  \begin{beamercolorbox}[wd=\paperwidth]{upper separation line foot}
    \rule{0pt}{2pt}
  \end{beamercolorbox}

  \leavevmode%
  \begin{beamercolorbox}[ht=4ex,leftskip=1cm,rightskip=1cm]{author in head/foot}%
    \texttt{http://www.texstackexchange.com}
    \hfill
    \texttt{xxxxxxxxxxxxx}
    \vskip1ex
  \end{beamercolorbox}
  \vskip0pt%
  \begin{beamercolorbox}[wd=\paperwidth]{lower separation line foot}
    \rule{0pt}{2pt}
  \end{beamercolorbox}
  \tikz[remember picture,overlay]{\draw[red, thick] ([shift={(1cm,-1cm)}]current page.north west)rectangle([shift={(-1cm,1cm)}]current page.south east);}
}

\begin{document}
\begin{frame}
\end{frame}

Update (20/04/2015)

Instead of repeating \setbeamertemplate in your main file or changing it in theme file, another option could be \addtobeamertemplate which works in this case.

Now the code is your code with border line inclusion and the result shows what I get with your theme file copied from Overleaf

\documentclass[final]{beamer}
%\usepackage{grffile}
\usepackage[framemethod=default]{mdframed}
\usepackage{showexpl}
\usetheme{I6pd2}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{psfrag}
\usepackage{amsmath,amsthm, amssymb, latexsym}
%\usepackage{times}\usefonttheme{professionalfonts}  % obsolete
\usefonttheme{serif}
\graphicspath{ {./img/} }
%\boldmath
\usepackage[orientation=portrait,size=a0,scale=1.4]{beamerposter}
% change list indention level
% \setdefaultleftmargin{3em}{}{}{}{}{}
\usepackage{tikz}
\providecommand\thispdfpagelabel[1]{}
%\usepackage{snapshot} % will write a .dep file with all dependencies, allows for easy bundling
\usepackage{pgfplots}
\usepackage{ragged2e}

\usepackage{array,booktabs,tabularx}
\newcolumntype{Z}{>{\centering\arraybackslash}X} % centered tabularx columns
\newcommand{\pphantom}{\textcolor{ta3aluminium}} % phantom introduces a vertical space in p formatted table columns??!!
\newcommand{\psihat}{\hat{\psi}}
\newcommand{\phihat}{\hat{\phi}}
\newcommand{\rt}{(\mathbf{r},t)}
\newcommand{\xt}{(x,t)}
\newcommand{\ket}[1]{\ensuremath{|#1\rangle}\xspace}
\newcommand{\bra}[1]{\ensuremath{\langle #1|}\xspace}
\newcommand{\elemm}[3]{\ensuremath{\bra{#1}#2\ket{#3}}\xspace}
\newcommand{\braket}[2]{\ensuremath{\langle #1|#2\rangle}\xspace}
\newcommand\psfragg[2]{\psfrag{#1}{\small #2}}
\newcommand\psfraggg[2]{\psfrag{#1}{\footnotesize #2}}
\newcommand\psfragggg[2]{\psfrag{#1}{\scriptsize #2}}
\newcommand\psfraggggg[2]{\psfrag{#1}{\tiny #2}}
\definecolor{darkgreen}{RGB}{0,100,0}
\definecolor{darkred}{RGB}{100,0,0}
\definecolor{darkblue}{RGB}{75,25,100}

\listfiles
\definecolor{darkgreen}{RGB}{0,100,0}
\newcommand{\myref}[5]{\textcolor{darkgreen}{{\footnotesize [#1 \textit{et al.} #2 \textbf{#3}, #4 (#5)]}}}
\newcommand{\myrefarxiv}[1]{\textcolor{darkgreen}{{\footnotesize [arXiv #1]}}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\title{My title}
\author{My name and coauthors}
\institute[A shorter name for my institute]{My institute}
\date{}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newlength{\columnheight}
\setlength{\columnheight}{105cm}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% This is the modified template. It needs two runs.    
\addtobeamertemplate{footline}{}{
  \tikz[remember picture,overlay]{\draw[red, thick] ([shift={(1cm,-1cm)}]current page.north west)rectangle([shift={(-1cm,1cm)}]current page.south east);}
}

\begin{document}
\begin{frame}
\begin{columns}
% ---------------------------------------------------------%
% Set up a column 
\begin{column}{.33\textwidth}
\begin{beamercolorbox}[center,wd=\textwidth]{postercolumn}
\begin{minipage}[T]{.98\textwidth}
\parbox[t][\columnheight]{\textwidth}{
% ---------------------------------------------------------%
% fill each column with content            
\begin{block}{}

\end{block}

\begin{block}{}            

\end{block}

\begin{block}{}      

\end{block}

\begin{block}{}

\end{block}
}

\end{minipage}
\end{beamercolorbox}
\end{column}
% ---------------------------------------------------------%
% end the column
% ---------------------------------------------------------%
% Set up a column 
\begin{column}{.33\textwidth}
\begin{beamercolorbox}[center,wd=\textwidth]{postercolumn}
\begin{minipage}[T]{.98\textwidth} 
\parbox[t][\columnheight]{\textwidth}{ 
% ---------------------------------------------------------%
% fill each column with content

\begin{block}{}

\end{block}

\begin{block}{}

\end{block}
\vspace{0.5cm}
\begin{mdframed}[style=innerleftmargin=20pt,innerrightmargin=20pt, innertopmargin=0pt, skipabove=0pt,skipbelow=0pt, linewidth=2pt]%
\usebeamerfont{block body}%
\begin{beamercolorbox}[leftskip=1em,colsep*=.0ex,sep=0.5ex,vmode]{block body}%

\end{beamercolorbox}
\end{mdframed}%
\vfill
}
% ---------------------------------------------------------%
% end the column
\end{minipage}
\end{beamercolorbox}
\end{column}
% ---------------------------------------------------------% 

% ---------------------------------------------------------%
% Set up a column 
\begin{column}{.33\textwidth}
\begin{beamercolorbox}[center,wd=\textwidth]{postercolumn}
\begin{minipage}[T]{.98\textwidth} 
\parbox[t][\columnheight]{\textwidth}{ 
% ---------------------------------------------------------%
 % fill each column with content

\begin{block}{}

\end{block}

\begin{block}{}

\end{block}

\begin{block}{}

\end{block}
}
% ---------------------------------------------------------%
 % end the column
\end{minipage}
\end{beamercolorbox}
\end{column}
% ---------------------------------------------------------% 
\end{columns}
\end{frame}
\end{document}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Local Variables: 
%%% mode: latex
%%% TeX-PDF-mode: t
%%% End: