A popular hack for Intel Macs involves creating a third FAT32 partition to hold your data, while using an NTFS partition to hold your Vista or XP installation. Problem is, if you want to undo this arrangement, Boot Camp won’t cooperate. If you’ve got good backups, and you’re brave enough to mess around with a couple command-line partitioning utilities, I found a way to restore your partitions to the way Boot Camp found them. Then you can use Boot Camp to put things back to a one-partition setup. Link