the Compaq Presario does not have BIOS tweeking capabilities, most are jumpers. If it is new enough, then you can jumper it up a bit, I think 500 is probably the motherboard's frequency limitation. If you have one of the mini tower, please note that the power supply fan is the same fan used for cooling the cpu which is so so. If you have jumper capabilities, you may want to lose the fan duct and put in an actual cpu HSF.
Know the exact Presario would help you locate the MB on Compaq's website.