I saw the same problem on GF6800 AGP video card. I tried Forceware version 78.01 , 78.05, 81.85, 81.87, and new 81.94. This problem occurs In 81.xx driver, but not occurs in 78.xx driver.
I always use default setting of Forceware, 1280x1024 resolution, and "High" setting in Lock-on display option. I tried to change Forceware settings (e.g. Filters, AA, optimization), display options (e.g. Texture), or BIOS settings (e.g. AGP mode, Fast write), but problem still occuers.
According to old replies, this problem seems to occurs in GF6800 system only. I have old GeForceFX 5900XT card, I'll try this. (If I can find the time...:icon_frow )