Jeez,
I had all the problems you people describe. I reinstalled XP but that didn't help. I pulled out my RAM and reinserted them one by one... and that didn't help. I swapped my videocard out ... no effect.
FINALLY, I uninstalled all my codecs. Reinstalled just two (ACEMegaCodecs and Dr. DIVX) and my sounds were back, nice and clean. BUT, the random reboots still occurred. THEN, while surfing on the internet, I found a VIA AC'97 driver that addressed this problem ( pb_alc650_5320.exe ). What did I have to lose? So I installed that.
No crashes since.
Could be a sound driver. Try the latest version... then an older version.
Dennis