Disable Windows Installer
Computer Configuration\Administrative Templates\Windows Components\Windows Installer
Disables or restricts the use of Windows Installer.
This policy can prevent users from installing software on their systems, or permit users to install only those programs offered by a system administrator.
If you enable this policy, you can use the options in the Disable Windows Installer box to establish an installation policy.
Never indicates that Windows Installer is fully enabled. Users can install and upgrade software. Windows Installer is enabled by default on Windows 2000.
For non-managed apps only permits users to install only those programs that a system administrator assigns (offers on the desktop) or publishes (adds them to Add/Remove Programs).
Always indicates that Windows Installer is disabled.
This policy affects Windows Installer only. It does not prevent users from using other methods to install and upgrade programs.