These programs can help you remotely monitor a computer (such as your own) without the knowledge of anyone using it.
Spector Pro A remote access program that has moved away from its original remote access Trojan horse roots. The current version of the program allows you to control another computer from a remote location. Shareware. (http://www.netbus.org)
PC Spy Monitor your computer while you are away by capturing and saving screen images. Shareware. (http://www.softdd.com)
Q-Peek View the desktop of a computer from anywhere on the Internet or on your local network using a standard web browser. Shareware. (http://www.qpeek.com)