I have a Pentium E6600 (2x 2,4ghz)
2gb ram
and a GeForce 7600 GT OC edition
i can run cnc3 on ultra high with the highest resolution >_< (1680x1050). Ok, i did turn anti aliasing off, cause that was causing some lag.. but all the other settings are at ultra.
So i think a 8600GT would be even better, and more ram cant hurt right? Especially when you run Vista.
I say, go for it!