Any Intel Core 2 Duo CPU will be fine with any of the nVidia GeForce 8800 models. Look at the PSU requirements for the video card before you purchase or build the computer. Also make sure the case has good airflow because you don't want to cram that video card into a really small case.
I don't know much about computers, so i don't really want to build it myself, but I'm trying to upgrade to play games. I originally just planned on buying a nvidia 8800 and sticking it in my old dell 8250, but now i think i want to buy a new, mid range computer and stick it in that instead. i was thinking of using an HP a1640n. The total cost of computer, plus video card, would be about 1500. the only thing i'm worried about is the processor, which is only an intel 6300. What do you guys think?