Instructions:

1. Click "Start" button
2. Click "Run..."
3. Type "regedit" + press enter
4. Navigate to "HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies \ System"
5. Create or modify "DisableTaskMgr"
   0 = Enabled
   1 = Disabled
6. Exit registry
7. Restart computer
8. Repeat step 1 to 7 for each user you want avoid using the task manager