I am running it on an Athlon XP 2800+, with 512MB PC2700 and a Radeon 9800XT
I am able to run it at 1024x768 with all settings raised above the medium. 6xFSAA and 8xAnisotropic and it rarely dips below 60FPS.
You should do fine with an Athlon 2500+, 512mb PC2700 and a Radeon 9600XT. Dont worry about sound card, get an Neforce2 motherboard with integrated sound. Its excellent.