the bios is absolutely nothing to be afraid of (with a few exceptions). you're going to have to go in there one day....whether its to turn off your onboard sound or change your boot device to reformat.
when your computer starts up just hit the button that it says will take you to your bios (often referred to as setup). the keys used to get in are usually - esc, the Fkeys - del key - a combination of keys.
once you are in, just look under all the sub menu's for something that talks about a front side bus or "FSB". just lower the numbers from whatever is already there to maybe 10 mhz less (remember, this part depends on the bios, it could decrease many different ways...from 400-333-266 or mhz by mhz)
if you think you changed something by mistake that you shouldnt have, just hit esc and dont save the changes....it will be like you never did anything.