You system specs are fine, so we can probably rule that out. Make sure you've patched it to the latest version (think it's 1.03) and also play with your compatibility settings (shout if you don't know how to do this).
Im running 64bit. I finally fixed the freaking issue. Turns out it was my monitor resolution being to high. I have a CRt monitor on the computer it was working and I used it on my pc and it worked just fine. I stumbled on another forum, a guy had the same problem with it. Turns out my pc is to good for the freaking game.