http://www.active-eraser.com/
download the one call Disk Wiper
Disk Wiper
Problem: Free disk space on your hard drive is not actually free!
It contains a lot of previously deleted files. Some programs writes
and delete temporary data on the disk. This activity can be
recovered!
Solution: Disk Wiper function overwrites all free space on data
storage. Use this function to prevent recovery of previously
deleted files or software activity.
its a free to try ware[/url]