This doesn't work on Vista(not sure about W7) by default but its easy to install.
1. Click Start then select Control Panel.
2. Select Programs and Features.
3. Select Turn Windows features on or off.
4. Select the Telnet Client option.
5. Click OK.
6. A dialog box will appear to confirm installation. The telnet command should now be available.
Anyways yea it's kinda cool.