I've had a number of hard drives wiped using Darik's Boot and Nuke (DBAN). However, I was rather dismayed to discover that that it was incompatible with the RAID 5 configuration on my IBM server. After trying a couple pre-packaged solution, I settled on using a more manual approach by booting from a LiveCD and running the command directly. The necessary command is "shred -vfz -n 100 /dev/hda", which I found here. I used the Fedora LiveCD since I had it, and since I knew it worked with my RAID controller. The only gotchas once you have the CD and command are: (1) you have to run as root and (2) it takes a bloody long time to write over a hard drive 100 times, even if it is a 15K SCSI!