how do I do that?
Actually, the easier way to see if it's over clocked is to look in your system properties by right clicking on the "my computer" icon/propterties. You'll come to your "system properties" menu. It should open the "general" tab first. There, you can see what OS and what service pack you have (if its NT, 2000, XP, etc.) If it's XP or after, you should see what your processor is, what it's clocked at and supposed to be clocked at, how much ram you have, who it's registered to, etc.
However, you can also go into your bios. Depending on what kind of computer you have, you can do it by tapping the Delete key, The F10 key, or what ever your system says to press when it posts (usually something at the bottom of the screen will say "setup DEL" or "setup F10, etc).
From there, you have to navigate to where ever your clocked speed is posted.. Sometimes, it's the first page it displays.. A lot of times, if you have a factory built system, you can't even overclock unless you get a different bios than what it came with when it was sold(Factory Built systems usually use there own bios like Dell, Gateway, Emachine, etc).
One thing you need to know is what your the speed of your processor is supposed to be so you'll know if it's over clocked or not.
I'm not sure if you know this, 99.9% of new systems will not be factory or shop over clocked in any way. Well, a PC shop(mom-n-pop kind of place) MAY over clock it for you if you sign a waiver voiding your warranty.
Hope that helps..