From Hero To Zero
You can download or buy utilities to wipe old disks clean and ensure any personal data is permanently erased. DBAN is one such utility, but there are ways, if you run Linux.
You can Zero disk contents using 'dd' command. Try this:
dd if=/dev/zero of=/dev/sda
The command will overwrite the first scsi or sata disk. For the second sata disk, it would be:
dd if=/dev/zero of=/dev/sdb
If you have ide disks, it will probably show up as /dev/hda or /dev/hdb. Use the mount command to check.
If you have an old disk laying around you want wiped clean, give it a try.
What have you got to lose apart from your data?