I would not recommend moving to Vista for at least one year.
So far, no one has seen any performance improvements with Vista versus Windows XP, and only heartaches. Vista may provide improvements in the future (after hardware and software manufacturers have really worked on trying to get better performance), but they are not there now.
So what can you do given most computers ship with Vista?
Even though these will cost you more money, I would suggest a computer specfically configured for music running Win XP. These companies have made sure that all of the components are compatible with each other
At least one of the companies above, PCAudioLabs, can even configure a "dual-boot" system (Vista and Win XP) using swappable hard drives. This would allow you to test out Vista while still using XP, eventually using only Vista. http://www.pcaudiolabs.com/vista.asp