How do I set up TFS PowerShell Snapin

Any chance you are running on x64? On my x64 system the Microsoft.TeamFoundation.PowerShell snapin only shows up under the x86 flavor of PowerShell. Adding it as simple as:

PS> Add-PSSnapin Microsoft.TeamFoundation.PowerShell

I take it that you installed TF Power Tools October 2008 release. If so, then there is also a shortcut on the start menu for a PowerShell console file that you can fire up. That preloads the TF snapin.

While installing Visual Studio Team Foundation Server 2013 Update 2 Power Tools .msi, I found that I had to re-install and select Modify installation and enable the installation of PowerShell Cmdlets .

@Keith Hill's and @Blakomen's answers are both correct; this and more information is available in the help file.

Start/All Programs/Microsoft Team Foundation Server 2010 Power Tools/HelpWindows PowerShell Cmdlets for Visual Studio Team System Team Foundation Server

Or simply

C:\Program Files (x86)\Microsoft Team Foundation Server 2010 Power Tools\Help\PowerShellCmdlets.mht

(Adjust as necessary for your install folder and version of Power Tools)

Note the following (from help Get-TfsItemHistory -full):

-Server <TeamFoundationServer>    Identifies the Team Foundation Server. This option is required if the command    is invoked from a directory that is not mapped to a workspace.