I have driver difficulties with my graphics card!?

I have a GeForce 7800 gs and am currently running windows 7 evaluation copy. The driver that windows installed by default worked good but not completely so. In games the polygons get stretched and the game becomes un playable. This happened before when I installed the newest drivers from nvidia, but somhow i got that fixed. I know that an older driver version runs best and doesn't make any graphical errors but don't know which to download! Please need help to fix this!