I suffer from a similar problem, if not the same problem. I first thought it was memory related so I ram memtest86 and found a bad stick of ram, chunked that. I replaced my processor because it was bad from the beginning. (I didn't find out the ram was bad until after I replaced the processor.) So I thought things would be smooth, boy was I wrong. I've tried every driver since 43.63 with no luck (yes, 46.20 as well), ran XFree86 4.3.0 - 184.108.40.2063 with no luck either. I've switched from Slackware current to Gentoo and it hasn't helped any, tried half a dozen different kernels and configurations with the same results every single time. I can only hope that I can find a solution by the time Unreal Tournament 2004 ships because I don't want to futz with this any longer. It's like I'm in a lose-lose situation with graphics cards, ATI drivers suck, nVidia drivers aren't much better either. *sigh* I'm at a loss as to what else to try.