Other then turning off trails and lowering your draw distance there is nothing much you can do other then getting a new video board or overclocking your current one. GTA is a hog when it comes to graphics.
but it is the first game to make me glad I bought a gf4
Yea, surprisingly it has run real well on my system, Celeron 500 384mb ram, geforce 2 mx 400. I turned off trails and frame sync and run the game at 1024x768 no problemo. Soldier of Fortune 2, however, is different, and is bordering unplayable using basically the same settings.
I think it basically stops the refresh rate syncing with the framerate (or something) - so theoretically you can squeeze out a few extra FPS, but yes you will see some tearing. I find it runs best with frame sync off, but Frame Limiter turned on. I'm running it @ 1600 x 1200, 32 bit with draw distance up 3/4 of the way and I've yet to see any slowdown. BTW, i think they've done a quality job on the graphics in this game - everything seems so much clearer than on the PS2.