ZZFH is correct. I had an AMD64 X2 4200+ and I had it at 800x600 with all details off and it struggled to stay around 25 fps.
I recently upgraded to an AMD Phenom II X3 720 and on my lowly ATI HD3870 Radeon, I'm running at 1280x1024 with most graphical options turned on and the game is VERY smooth, and that's on just three cores.
I've since unlocked the fourth core in my CPU (with no issues so far!) and the game runs pretty much the same as far as I can tell. I still can't play at the highest settings (I think I'm GPU bound now), but with what you have, the game will be barely playable and it will look like crap.
BTW ZZFH! Love the pug picture!