With your stats, I'd probably seriously consider the X-box version. I've played through it on a duron 1200 /256 MB / geforce 3 ti 200 and it was passable, though far from ideal. Assuming you've got an x-box and live, there's no reason to use the pc version instead. It's main advantage is that it has much better graphics and audio if your system can hack it - and yours isn't going to be able to.

Featurewise, if you've got X-box live they're practically identical. Mods for the PC version just aren't overwhelming either. Controlwise...well, matter of taste. I thought keyboard and mouse kicked the tail of the gamepad control, but it's essentially a matter of what do you like better.