what is the exact model of mtherboard
Have you tried the latest drivers off the site?
http://www.abit.com.tw/page/au/moth...1ty+FP-IN9+SLI&fMTYPE=LGA775&pPRODINFO=Driver
Try downloading the drivers from Realtek's site?
When I installed XP SP3 on my grampa's laptop (Toshiba), the drivers I got from Toshiba's site simply didn't work... it was a different kinda problem, though, everything seemed to work but I just didn't get any sound. Downloading and installing the drivers from Realtek's site fixed it.
Maybe worth a shot?
Try installing the UAA Bus Driver for High Definition Audio.