Should be able to use anything from socket 939, which only went up to an Athlon X2 4800 or something along those lines. The only problem is 939 ended production years ago, and finding anything new has become about impossible. There is always the used market, but even than people charge an arm and a leg. In a number of cases, it's cheaper to purchase a new dual core/motherboard/ram than it is to get a slower out dated socket 939 processor.