BleepingComputer.com: Gta San Andreas Very Laggy, Oddly.

Oddly, GTA San Andreas is running very slow on my pc, even with nearly minimum settings. trying to run at 800x600 with min drawdistance, min detail, and no AA. it'll run fine in open areas, but when it comes to driving in cities or on highways in a fast car, it lags horribly. often getting as low as 1 or 2 FPS. the lag is even sometimes causing the NPC cars to crash into each other as they pop on screen.

My specs are in my sig. Its a clean install of XP that i did about a month ago, have made sure i have updated drivers for everything, and the game is freshly installed as well. all other games i have tried on it since installing xp run fine, like oblivion with maxxed setitngs and modded to have higher detail meshes and textures. yet san andreas wont run even on lowest settings. it even gets odder, when i had 64bit Vista on the pc, san andreas ran flawlessly with maxxed settings. back before i had vista, when i had 64bit xp and a core 2 duo cpu and a 7600gs, i recall it running fine as well.

so why is it not running good now with the specs in my sig?
is there anything i may have over looked?