You sure about your CPU product numbers and speeds? The E6600 is a 2.4GHz part, not a 3GHz part.
There are faster Core Duos (E7xxx), including a 3GHz part, but they are not compatible with your board - you are sure it's a 6600, not a 7600?
Have you got the S-spec number to hand? Scribed onto the metal top of the processor package.
SD