Well Windows XP Professional has a built in telnet server. To enable it go to Start, Control Panel, Administrative Tools, Services, and scroll down the list for telnet. Double click it, set the Startup Type to automatic, and click the "Start" button. This starts the service, and sets it to automatically start every time you start windows. If your computer doesnt have a telnet server go to http://kpym.sourceforge.net#4
and download "KTS v1.06 Setup" and save it to the desktop so you know where it is when it finishes. When it finishes downloading, install it, go to Start, Control Panel, Administrative Tools, Services, and find "KPyM Telnet Service". Double click it, set it to start automatically, and click start. That starts the service, and you will be able to connect to that computer with telnet on port 23 and be able to remotly shut it down.