When you first try to run a telnet command, Windows will informs you that telnet is not recognized as a command. Telnet Client is a feature included with Microsoft Windows Server 2008 and you can install Telnet Client by using the Add Features Wizard in Server Manager.

To enable Telnet on Windows Server 2008 follow these steps :

1. Open Server Manager, click Start > Server Manager
2. From the left panel in Server Manager, click on Features
3. Click on Add Features, as you can see i have not installed any Feature on this Server ( 0 of 34 installed )
4. From the available list of features, scroll down and select Telnet Client, then click Next
5. On the Confirmation page, click on Install.
6. Installation of the selected feature will be initialized and started.
7. Once installation is completed, click on Close.

Now open Command Prompt, and run the telnet command

As you can see, Telnet is now recognized by Windows Server 2008 and you can start using it to connect to your telnet servers.