That's sounds like an excellent computer so far. Most mobo's (especially the newer ones that support the barton's) will have USB 2, probably about 6 of them.
As for hte sound question, I think Audigy 2 is slightly better, not sure though. Whichever one is 24-bit. If they are both, go for the one that has more extras.
EDIT: Also, if you're gonna pimp out hte rest of your comp like that, I'd go ahead and upgrade to a gig of memory
.