For gaming you pc should be good enough. Basicly you could overclock your CPU to get extra performance, so you could upgrade your CPU cooler. I'd recommend the scythe mugen 2 cooler, as it has brackets for nearly every motherboard socket, for future upgrades. It is also one the best CPU coolers for a small price.
Your 4 gb of ram should be more then enough for now. If your framerates aren't high enough you could always upgrade your Gpu, but I'd hold out on that until nvidia bring out their new gpu! I'm sure ati will cut prices a bit. I hope that helps for now!