After a fresh install of Windows 7, I typically install additional features of Windows 7 by using the DISM (Deployment Image Servicing and Management) tool. You must open a command prompt as administrator before using DISM.exe.
dism /online /get-features
This will show me available features to install on the system. To install a feature, in this case Telnet Client, I will issue the following command:
dism /online /enable-feature /featurename:TelnetClient
Note: The featurename is case-sensitive.
I create a simple batch script to install common features I use in Windows after a fresh install and TelnetClient is one of them.
Refer to http://technet.microsoft.com/en-us/library/dd744582(v=WS.10).aspx for more information.