Well seeing that you have a dell more than likely the BIOS is locked.
But with a PC like mine for example you could go into the BIOS and do it. Raise FSB, voltages etc. etc. Or some programs will do it in the GUI, for example NVIDIA NTUNE, or ASUS AIBooster.
I would not recommend it if you don't have a good CPU cooler or good airflow in your case.