Unfortunately, what nemowolf said is true...the OP will definitely need to look up some very specific specs on the motherboard to see if it supports the Core 2 series. If you want to upgrade the CPU, that is.
But, I don't think it's necessary. I have a friend whose system contains a stock Pentium D at 2.8GHz, 2GB of RAM, and an 8600 GT, and he's pretty happy with performance in Oblivion and Company of Heroes. The PD is definitely okay if you're not a really hardcore gamer.