Although the MNF eigenvectors are not exactly the same as PCA eigenvectors due to the noise whitening that is performed with MNF, I believe you can still consider the eigenvectors as the contributions to each PCA band.
This help article discusses the MNF statistics files, which are a little different than PCA:
http://www.harrisgeospati...D/19433/Default.aspx And this help article discusses how to convert PCA eigenvectors to "weights''::
http://www.harrisgeospati...D/19426/Default.aspx The eigenvector matrix will contain the eigenvectors as the rows with the columns representing the band contribution for each vector.