A lot of newer hardware is not supported in WinXP; in other words there aren't drivers available. But like Paul said he was able to downgrade his Toshiba to XP with no apparent problems but every situation is most likely different. You could try it, back every thing up you don't want to lose first and if it didn't work then you could always restore your computer back to Vista using the restore CD or partition that should have came with your computer.

Best of luck!
Bill