Windows 7 and Windows Vista, both come with Telnet disabled. This is due to security reasons as Telnet is highly insecure and you should preferably keep it off too. However, you can easily enable Telnet:
- Go to Control Panel
- Open Programs and Features
- Open Turn Windows features on or off from a link in the sidebar
- In the dialog box that appears, scroll down and find Telnet Client and check its check box
- Click on OK. Wait till Windows saves the changes.
- You can now open Telnet as usual by typing Telnet in Command prompt