I recently came across this utility that allows you to securely wipe hard disks.

"Darik's Boot and Nuke ("DBAN") [1] 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 is part of the National Nuclear Security Administration suite of security tools and is available in both Floppy and CDR/CDRW versions.

[1] http://dban.sourceforge.net/