The answer to how do you wipe it depends on what you had on it.. If you have files that you would be embarassed by should they land in the hands of the police, or the evening news... Then I recommend replacing the hard drive, do a RESTORE using the restore CD's that came with the computer and "De-Militarzing" the original hard drive.
That involves hammers. anvels, explosives, flame throwers and other various and assorted means of reducing the orignial drive to it's constituant atoms.. NOTE: this is not a joke, it is how the army does it. (Actually I'm holding back a bit, they are much more destcrutive)
However if you are like me.. Don't put on the HD what you don't want on the NEWS.. The programs above are good... If you have the "Out of the box" CD's use them.. If not ship it with a generic Linux distro (Downloadable type) or just ship it NO O/S