Haha, where in the world did you get that idea? Sure, the dual cores aren't as good as say, a single core FX-57 at gaming, but they aren't bad. Truthfully, his system is probably better than one with an FX-57, because it has all that multitasking power and the difference between games between the two is probably not all that high, though it will be noticeable. Overclock that bad boy!
I have similar specs as you. Don't expect to have a "gaming" computer with a 3800 X2. You have a computer that kicks ass, it just so happens that that includes gaming. Oh, and your 7800 wont hurt either. Gaming computers OWN at gaming, but arent as good at other things.