Kingcarcas... dont' know if you can still find them but do a search for daniel_k's drivers for vista. They work great. Unfortunately I only have the Audigy 2 ZS drivers backed up. Maybe someone here has the ones for the X-Fi stashed away. I've not been too impressed with realtek audio, it was relatively crappy on my previous board compared to my Audigy 2 ZS - background noise and just not as clear.

In XP I believe that either GPU client requires a whole CPU core. Just the way XP handles CPU processing.