I am not sure how princomp works, but here is a quick way to do this.
1) mean center your data, meaning subtract the mean across all data points across each dimension from each dimension.
2) [U,S,V]=svd(Data,0);
3) Assuming your dimensions are across columns (meaning your data point are row vectors), PCA weights are U*S, your variance vector is diag(S^2), your PCA vectors are S*V'.
Your results wont be normalized in any way, but they will be centered, and that is desirable in most cases.
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