Three sure-fire ways to wipe a drive:
1: If you want to save the drive, buy an eRazer.
PC Connection - Drive eRazer for 3.5" IDE PATA Hard Drives- Standard Model
2: If you want to physically trash the drive, take the cover off and expose the platter to ambient air. Once you contaminate the platters with dust/debris, the drive is unusable. At 5400RPM and higher, a little piece of dust will tear the drive up if someone attempts to put it back together and run it. Once disassembled, you have lots of options: such as whacking it with a bat, a hammer, or drilling holes through the platters.
3: Install XP, IE6 and no virus checker/spyware blocker and let my 7 year old son surf the Web.