I don't think socket 939 has a quad core, but what would be your goal? If you could save some money and put together a budget build you would get far more out of it then spending money on a much older system.
YOu can get a motherboard that will run any Quad AMD for about $50.
Check out 760G's if your on a budget. It also has onboard video if you need that.
Make sure it has enough dimm slots and ide connectors for your needs.