Sounds very odd. Could possibly be a bad chip...don't know. Are you running with aggressive RAM timings (if so, back them off, if not...you're good). Do you have fastwrites and sideband addressing enabled? If not, enable it, if so, disable it. I've heard that it can lead to problems on some systems, while on others it speeds it up (I have both disabled). I do have a better vid card than you, but RTCW is flawless on my machine, as is MOHAA, ~60fps constant at 1280x1024 in MOH. My 3DMark2k1 is 8103. Something seems wrong, though, since my 3DMark score was about the same as yours when I was running the same setup and a GeForce 2 MX! However, even then, RTCW was relatively smooth.
Hope you get it figured out.