How can I securely wipe a hard drive?

Duke wants to replace his hard drive. How can he get wipe the drive securely before recycling it? Leo recommends Darik's Boot and Nuke (DBAN). It uses military-grade erasing techniques to completely wipe the drives. What about those computers that aren't running? Leo says to take them out of a non-working computer and use a universal drive adapter by Newertech. Then you can connect it to a working computer and wipe the drive. You can also use SDelete from Microsoft's Sysinternals package, but go with DBAN.