How do I wipe my hard drive and then install a new os?

I have a laptop with some nasty infections, and I want to wipe it completely clean (there's nothing on it I need) and install a new OS. I have the install disks for the OS. What's the best way to do this? Ideally I'd like to use Killdisk, but I've never used it before and I'm afraid I will end... show more I have a laptop with some nasty infections, and I want to wipe it completely clean (there's nothing on it I need) and install a new OS. I have the install disks for the OS. What's the best way to do this? Ideally I'd like to use Killdisk, but I've never used it before and I'm afraid I will end up with a heavy paperweight, unable to install the new OS after using it. Suggestions anyone?
Update: Just to be clear, I want to WIPE the drive, not reformat.
Update 2: Let's pretend I'm selling the computer, so I HAVE to WIPE the drive. Not reformat. Wipe. I am installing Ubuntu after getting rid of XP.
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