On my 2010 15" MacBook Pro, the DVD drive is on a separate SATA controller from the OEM hard drive. I wonder if that presents a problem? I'm not sure how the Mac treats that second SATA interface (say as an external interface though it's physically internal to the machine). Vista is very picky about being installed on an external drive and it needs drivers if it thinks the drive is on an external (eSATA) connection rather than internal SATA (strange, I know).
-------------------- Lisa Gade Editor in Chief, MobileTechReview