I've been researching some and I found the best CPU that supports socket 939 is an AMD Athlon 64-Fx60, it is dual core, would it be compatible with just the same socket or are there other things it needs to be able to work?
It's all dependent on the BIOS and what IT can support. Yes, there were better CPU's on Socket 939 than an Athlon 64 X2 4800+, BUT, as I alluded to earlier, since that's an OEM motherboard that has VERY limited CPU support, unless there's a BIOS update that provides support for anything better, that's the best you can do.
That's the main reason I wish people would just learn to build their own systems, lol. SO much easier to upgrade, with a MUCH better upgrade path usually. I understand building a computer seems out of most people's leagues (it's really not. It's extremely easy, in fact), but man, it's worth it, and cheaper too, most of the time.