If like me you use telnet a lot, you’ll have been surprised when the command wasn’t available to you within Windows Vista. This is because Microsoft have taken telnet out of the default Windows Vista installation, and made it a feature which you have to manually install.
Installing telnet within Vista is simple, though, and only takes a few minutes:
Start by opening Control Panel and then go to Programs and Features
Then once open, down the left-hand side, you’ll see an option Turn Windows Features on or off – go into that.
Then scroll down in the list and check the box next to “Telnet Client” and click OK. Windows will then install telnet, and you’ll be able to run it from a command prompt as normal.

You could, of course, download PuTTY and use that instead of the Windows version of telnet, and benefit from a wide range of additional features.