Just click the Start button, and go to My Computer. Once you're there, right click the hard drive that contains the Operating System (:C Drive, I think). Right click it, and then select Format. Confirm everything, and then it will wipe the entire hard drive - possibly including the Operating System. Be very careful. I've never wiped my hard drive before, so I don't really know.
One tip though : DO NOT DELETE SYSTEM_32!
System_32 is where the OS is kept. Do not delete this folder, or there will be nothing on your computer. People are trying to recreate a previous incident where some kid had a probem with sprites. The kid was told to delete System_32. He did it, and he no longer has a computer.