You can download a utility to invoke the drive's own Secure Erase command. This is a better erase than DOD overwrites. Here's the paper from the National Institute of Standards and Technology that says so: http://csrc.nist.gov/publications/nistpubs/800-88/NISTSP800-88_rev1.pdf.
I personally boot the Parted Magic disc to do secure erases. Remember to set a disk password first and remove it afterwards.