I am not really sure, but this is what I would do instead. When you installed Vista then make sure that you choose FAT 32 instead of NTFS. That way OS X can see and edit Vista folders. But unfortunately Vista can't see HFS format...
P.S. This is what I have done in XP I am not sure if this will work for Vista.
I don't think you can install Vista on Fat32. You could however create a third partition which is FAT32 which will then be able to write to and fro between OSes.
Or you could download this ntfs for mac (beta) and read/write files on your Vista partition...
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