The first thing Leo suggests doing with this computer is formatting and reinstalling Windows. This is an old computer, so he may want to consider putting linux on it. Leo recommends installing Puppy Linux, which he can download for free, and put on a USB key or CD. Then he should boot to that USB key or CD, and completely format and overwrite the drive to get rid of the other person's stuff. Then install Puppy Linux.
Utah Roger in the chatroom says he can call Dell and ask them to send recovery discs for about $10.