You would need a Socket 939 compatible motherboard, prefebly with an nForce chipset. There is a lot of different boards you can get.
You can get a no frills motherboard like this. It is still a great overclocking board though:
http://www.newegg.com/Product/Product.a ... 6813127225Or all the bells and whistles:
http://www.newegg.com/Product/Product.a ... 6813131568Also, if you are building a 939 socket computer, buy DDR ram instead of DDR2, because DDR2 is not supported. I didn't know this when I was planning what to buy for my build. Nothing wrong with 939 and DDR RAM. It is a little cheaper than AM2 and DDR2 and the performance is pretty much the same.