In case anyone else runs into this, it's a bit weird. I contacted Mathworks support, and apparently this is a bug in their purchasing process.
First, make sure you upgrade to Student Version (SV) R2011a for Mac OS X, 64-bit. Once you have that installed, go back to the purchasing page for Student Version and this time select Windows as your operating system. Choose the Image Acquisition toolbox from the add-ons for SV R2011a for Windows, and go ahead and download it. You will get an email that directs you to the download page, and when you get there you can choose Mac OS X 64-bit as your true operating system, and the files you end up with should be for Mac OS X.
I assume the Mathworks will get this fixed at some point, but until then this is how to get around it.
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