As to what you can adjust to get better performance, well, first off, the minimum requirements is for a 2 GHz dual core processor, so you are well below that currently!
There really is not anything you can do to circumvent that, but disable shadows, dust effect, extended drawing and physics ingame and hope for the best.
missed the fact that it was a dual core in reqs. ill check out that processor you mentioned. i know 939 socket processors have been discontinued so should be fun to locate one.

Maybe it's time for a new board'n'stuff xD
AM3 Mainboard+4GB RAM+fast dual core cpu is only ~150 real life gil.
I've had this rig for 6 years now. been meaning to replace it for a while now. hard to do atm though, in my last semester of college.

in grand scheme of things i only paid $15 bucks for the game so no great loss if i can play it.