I run it beautifully on my 3500+, 2Gb DDR400 and X850XT. Its perfect in all resolutions.
My son has 2700+ XP, 1Gb DDR400 and a Ti4200. I expected it to be jerky. It wasn't. Tried it on 1024x768 and it was smooth and fast. BUT the blood looked funny, couldn't notice his shadow and not much smoke filling the room during gun battles. And the opaque glass window on the door looked funny.
So it was just detail really.
However another freind has a 2000+ XP, 512Mb DDR400, 9600Pro and it hesitated a lot and took ages to lload. Didn't sticka round to watch his battles - probably sad - tthat was on 800x600.
SP Ti4200 owner - just get a bit more ram!!!