I have a the DC5750 version of your computer, and I've upgraded mine to the fullest extent.
These Compaq machines were built for Business use only, not gaming, or video editing, or anything remotely close to that. They were made for word processing and viewing files for the most part. HP doesn't manufacture their boards, so another company builds them with the specifications HP includes, one of these specifications is for Core Multiplying and Voltage changes to be locked, therefore you are unable to overclock your system.
Heat will also be a problem if you have a stock cooler.
In conclusion, you will be unable to overclock your DC7700 through BIOS or software.