Vista actually makes high-end audio hardware less important than it used to be. AFAIK, the way it processes audio basically bypasses a lot of the hardware-based acceleration (a la EAX) on many 'premium' sound cards.
Of course, that's just what I've come to understand from cursory research, and I could be way off the mark.
I 2nd the M-Audio suggestion, I've used many of their products with outstanding results.