Microsoft Windows Vista doesn’t install telnet client by default.
If you want to install telnet client by yourself.
1. Control Panel -> Programs and Features
2. Click “Turn Windows features on or off”
3. Choose Telnet client and ok.
References:
http://www.windowsitpro.com/article/telnet/where-is-the-telnet-client-in-windows-vista-.aspx
http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol