Undo Another User's Checkout In TFS 2010

tf undo /workspace:machineName;domain\acct $/TeamProject/Path/To/Files/* /server:yourTfsServerName/TeamProjCollection

Sometimes I'd see an error returned: TF249051: No URL can be found the corresponds to the following server name: Verify that the server name is correct

Try including the full URL to the project collection:

tf undo /workspace:machineName;domain\acct $/TeamProject/Path/To/Files/* /server:http://yourTfsServerName:8080/tfs/TeamProjCollection

Or maybe you'd rather nuke the user's workspace,

tf workspace /delete machineName;domain\acct /server:http://yourTfsServerName:8080/tfs/TeamProjCollection