Looking for a disk-wiping program, preferably one that meets the U.S. Department of Defense's standards for disk sanitation? The DOD suggests that a hard drive should be wiped clean seven times so these programs will overwrite your entire hard disk with data multiple times, ensuring that the original data can't be retrieved. I hope you can be patient because it can take several hours to wipe the hard disk.
One to consider is Darik's Boot and Nuke which is free down loadable software that creates a boot disk which wipes everything cleanly on the hard drive. It can be used with floppy disks, USB flash drives, as well as CDs and DVDs. A similar program is Eraser which I have not seen or used so at some point I may be able to compare the two.