Go on another computer, get a blank disc like a CD-R, CD-RW, DVD-R, or DVDRW and download an iso image of Windows 7/8, burn the iso image to the blank disc, put it into the windows xp computer that you want to wipe the hard drive on and boot from the disc. Once the windows 7/8 install screen has come up, click next, click install now, accept the terms, click on custom (advanced), a "Where do you want to install Windows?" screen should come up. when it does, choose the hard drive that xp is installed on, and hit format. If you think that it has been formatted, shut off the computer, turn it back on and boot from the hard drive and see if windows xp still remains. You will know that it doesn't if either nothing happens, or it'll say...