I suppose the other one is a X2 which would be a dualcore. Dualcores have lesser coreclock at higher efficiency than single cores. your X2 should run run like a 3ghz single core in single core applications.

I don't know what you want to upgrade and how much money you want to spend, but I'd say, get a new board and a nice intel Quadcore. The q6600 should be around 200 dollars to get which is neat. Quadcore speed elevates you to a whole new level of detail and it's just more to play around when you have 3 times faster preview-renders.