Erase your hard drive with Eraser

Erase your hard drive with Eraser: "Just deleting files isn't enough. You need wipe that hard drive clean to make sure that your data is completely gone. Eraser is a tool that can help you do just that. Not only does it 'erase' your data, it actually overwrites it with other data in such a way that it's really, really gone. Now you can sleep better at night knowing that your personal information isn't going to fall into somebody else's hands.

Eraser is a free download. It's a Windows app and the latest version runs under XP and later; they've also got an older version that still works with Win98, ME, NT and 2000."

http://eraser.heidi.ie/