Hi
If you want to ensure no one can recover or undelete any data on your hard disk consider using DBAN to over write all of hard disk space
then re installing from Windows DVD
alternative mentioned above create a new user account (admin)
login to new account and delete all other users accounts .
empty recycle bin
disable System Restore to clear space, then reboot and re enable System Restore
run cc cleaner to clear out Windows temporary files including empty recycle bin and clean out some registry history
finally use (Heidi) Eraser to overwrite free space on hard disk
(Eraser does not seem to work fully on Vista & 7)
This method is quicker as you can easily spend a day Installing Windows, programs, anti virus software then running Microsoft Updates etc
regards
Mike Barnes