In the build Yami posted? Yes, as long as it is a LGA775 processor. In other words, a socket 478 Intel P4 will not work in it (different socket). The E8400 is a 3.0GHz CPU, by the way, but I think you meant you already have one maybe?
A 3.0GHz Intel will not work in the build I posted as it is an AMD build, which is a completely different animal (and socket). The GA-MA770-UD3 will run any AM2/AM2+/AM3 CPU on the market, but will not use DDR3 RAM like a native AM3 board would.