Help w/ Video Card Please!!

I am having some serious problems when i play Counter Strike, which is when i start to play after about a half an hour my guy starts to move in slow motion and everything is all messed up to the point i have to exit the game. I have a geforce2 GTS by visiontek, running a 1.2athlon asus a7m266 mobo, 128ddr mushkin ram. any suggestions?

If it always takes about the same amount of time before things start messing up. It might be a heat issue. Install a hardware monitor program and check the temps of the mohterboard and cpu.