Instead of going through the long-winded way of installing features using Server Manager, you can install PowerShell quickly in Windows Server 2008 from the command line using the following command:
servermanagercmd -install powershell
Why use the GUI when the command line is much quicker?
Other posts which may be of interest..
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Installing the Telnet Client on Windows 2008 using a Command Prompt
How to Turn off IE Enhanced Security in Windows Server 2008
Viewing Previous Command History in Windows Command Prompt (cmd)
What is Aero Glass Remoting? Terminal Server Aero Glass? (Windows Server 2008 R2)
Finding the Uptime of Windows Server 2008
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