well, most computers that are brand name won't allow you to. first check your bios and look if you can edit your processor front side bus. If not, then the bios doesn't support it. the board might not either.
don't actually change it, but tell me if you have the choice to change it.
also, you'll want to buy an aftermarket cooler if you're going to overclock.
<update> Thorson Beat me to the point by a little bit :P