Hi, Sloth! I seem to have the same exact problem as you do.
I have a Club3d 6600GT AGP, with P4 2.6, can't remeber which MOBO (I'm writing from work). PSU is the one that came with Antec Sonata case. Latest official drivers from NVidia. WIN2k + SP's.
With 1024x768, 2xanisotropic and 2xantialiasing KOTOR2 runs like a dream. With 4xanisotropic I got the same glitches as you did after about two hours. With higher resolutions KOTOR2 was playable for maybe 30 mins. After that the game looked like your screenshot.
It's a new card, so I haven't tryed it with much else than KOTOR2. Ghost Recon we played online for hours, 1280x1024, absolutely no problems, so I believe it can't be temperatures or my powerless PSU (though it's an older game).
But I just checked what the release notes for the latest NVidia beta drivers said:
"Issues Resolved in Version 67.03. GeForce 6600 GT AGP: Fixed a 3D corruption problem that appears when this card is used with certain motherboards, such as SIS motherboards.""
So could it be, that it's just a driver problem?