Secure File Deletion
From Windowsxp
The Recycle Bin just isn't acceptable for deleting files. The files aren't actually deleted, and may remain on your hard drive for quite a while. The solution is to practice secure deletion.
Several programs are available that can destroy your files beyond the point of recovery. Some file recovery software is listed here as well, but keep in mind, you will not be able to recover securely deleted files.
File Deletion Programs
Ultrashredder
File Recovery Programs