You need to go to ASUS's site and look for a compatiblity listing.
What type of socket is it? 939? AM2? If 939, you're options are _very_ limited since those processors aren't being made anymore and the supply of faster dual core 939 chips is really drying up. You can find them used but at a price premium. In fact, the high resale prices for 939 chips has me considering selling off all my 939 systems (#3 and #4 in my sig) and building cheap low power intel rigs in their place. I probably won't, though, since that involves quite a bit of work, would put me out of two computers for a few days and both machines are more than capable of doing their jobs. So why bother?