Graphics glitches

When playing opengl games (Jedi Knight2 & C&C Renegade) i progress through the game and about an hour or so into the game i get these flickering rainbow colours on the textures. It isnt an overheating problem because if i turn my comp off overnight and then try to play the next morning, same problem. However if i load a previous level, the graphics are fine (i have tried reinstalling the games too, to no avail.)
I did fix the problem in JK2 by disabling “GL Extensions” in the video setup, but this isnt an option in C&C:Renegade, can anyone help me?

Athlon 1Ghz
VIA KT-133 Mobo
GeForce2 MX400 64MB (tried manufacturer and 3 different detonator versions)

I was looking at ur post and You and I have the same problem. But my video card inwhich is a Geforce4 Mx 420 does it to all my games but 1.

I have emailed tech support for the card an when i get a reply ill post it.

They reckon its a memory prob (on the card) so i might just take it in and have them check it out