Exactly
I know exaclty wot ur problem is. Basically, your graphics driver is too new (if that can be possible). At an educated guess i would say you are running your 6600 with the nVidia 66.91 driver. This is too new, downgrade slightly to version 61.77 which is flawless in every way with 99.9% of vid cards. The same thing happened with me. Now my sytem never crashes....EVER. I can play HL2, UT2004, everything with no glitches or crashes.
Hope this helps