Darik's Boot And Nuke looks like just the thing. Plus it deals with filesystem caching.

Darik's Boot and Nuke ("DBAN") is a self-contained boot floppy that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect, which makes it an appropriate utility for bulk or emergency data destruction.

It's also avaliable as a bootable cdrom image. However you save it, be sure to label it very clearly. :)

-- Rocco Caputo - rcaputo@pobox.com - poe.perl.org