Go to MMC start the Computer Management MMC snap-in and/or Start - Programs - Administrative Tools - Computer Manager Expand the 'Services and Applications' branch Select the Services leaf Right click on 'Telnet' and select Start You could also right click and select Properties and set the startup type to Automatic so it will always be started. Click OK
To start from the command line use

C:\> net start tlntsvr
The Telnet service is starting..
The Telnet service was started successfully.

The telnet service uses %systemroot%\system32\tlntsvr.exe so if you wanted to stop it being started on a machine you could set an ACL on the image or delete.

Unlike normal Telnet services passwords are not set clear text and are encrypted using NTLM. You need a special client which is provided with Windows 2000 Professional