I have a Core2Duo 2,4 Ghz running with 4 (3 because of a 32-bit OS) gb DDR2 Ram at 800 MHz, and Far Cry 2 and Fallout 3 ran beautifully. Crysis wasn't as smooth, though.
I think whether or not you can rún the games boils down to the GPU, which I'm not familiar with. F3 and FC2 and Bioshock...