Can't overclock on 750i

My problem is, I can't overclock my 6600 quad on my asus p5n-d 750i motherboard. I know it's not exactly the motherboard I'd want to overclock on, but I figured I'd get to at least 3.0ghz. This is not the case, I can't get over 2.5 ghz on this board. Seeing as the factory settings are 2.4, that's pretty damn bad. Any suggestions, or links to OC drivers would be APPRECIATED alot.

EDIT: AT LEAST point me in the right direction for the latest bios update.