When you install run the AD FS 2.0 setup (AdfsSetup.exe) on Windows Server 2008, the PowerShell feature, which is a prerequisite of AD FS 2.0, may not be installed, even though the installer indicates that it will be.
When setup attempts to install the PowerShell feature, you will see this:
However if you do not see setup installing the PowerShell feature, and when setup completes PowerShell is in fact not installed, it may be because the following registry key existed prior to running AD FS 2.0 setup, even though the PowerShell feature was not currently installed:
HKLM\Software\Microsoft\PowerShell\1
You could uninstall AD FS 2.0, delete the HKLM\Software\Microsoft\PowerShell registry key, then rerun the AD FS 2.0 setup, but if AD FS 2.0 setup did not install the PowerShell feature, you can simply install it from Server Manager. From within Server Manager, select Features, then Add Features, then check Windows PowerShell and click Install.
You can also run servermanagercmd.exe -install PowerShell from a command prompt to install the PowerShell feature.
AD FS 2.0 PowerShell cmdlets are available after you run Add-PsSnapin Microsoft.Adfs.PowerShell from a PowerShell prompt.
You can view the available AD FS 2.0 cmdlets after you add the snapin by running Get-Command *ADFS*