Disable Task Manager
User Configuration\Administrative Templates\System\Logon/Logoff
Prevents users from starting Task Manager (Taskmgr.exe).
If this policy is enabled and users try to start Task Manager, a message appears explaining that a policy prevents the action.
Task Manager lets users start and stop programs; monitor the performance of their computers; view and monitor all programs running on their computers, including system services; find the executable names of programs; and change the priority of the process in which programs run.