Hi, Telnet isnt very helpful in the Windows environment as you would need to know the command line options for many of the things you do through GUI. However, in Win2000 you'll need to enable the Telnet Services. Go to Admin Tools and you will find telnet services there. For Win 98, it doesn't have a telnet service by default. you will need to search and install some third party telnet server for Win 98.
However, if your aim is to manage on m/c while sitting at another, then go for a freeware tool called VNC (http://www.uk.research.att.com/vnc/). It'll be much better than using telnet and you can manage your other machine through a web browser only.