One of the biggest problems that faces dual-booters is data corruption on many different fronts

One such “feature” is that those dual-booting Windows XP and Windows Vista will find that every time they boot into XP, they’ll lose all their Vista system restore points - because XP “intelligently” detects them as being corrupt XP system restore profiles. So much for painless dual-booting. Even Vista’s “Complete Backup” feature is decimated by the very existence of XP on the same computer - and having them on separate hard drives doesn’t help!

Check This Link For Solution:
How-To: Hide Vista Partition from XP with NeoGrub! at The NeoSmart Files