I recently built a new PC which had an integrated Realtek HD Audio codec. I was a bit wary about using onboard audio given quality concerns with the output and drivers. The quality is actually pretty good, however the drivers regularly crashed on me in games. With a bit of poking around, it turns out parts of the rtkhdaud.sys driver are not thread-safe, as a null pointer dereference occurs after a test for such. I created a really nasty hacky patch that adds a second null pointer test before writing to memory, which seems to have resolved the rtkhdaud.sys stop errors I was getting. Maybe it works for you too, maybe it won't :).
You must be using the Realtek drivers (www.realtek.com.tw), not OEM drivers. The driver version must be R2.14 (January 2009). For 32 bit Windows 2000/XP/2003 only. Replace the rtkhdaud.sys in your windows/system32/drivers/ folder with this: RtkHDAud-R2.14-Hacked.zip (2.39 MiB). Use at your own risk.