* Click Start, type gpedit.msc and press Enter
    * Go to the following location:

    Local Computer Policy | Administrative Templates | System | Logon

    * Set Hide entry points for Fast User Switching to Enabled
    * Quit the Group Policy Editor.

By enabling the policy, Administrators hide the Switch user button in the Logon UI, the Start menu and the Task Manager. Note that the Group Policy Editor does not exist in certain editions of Windows Vista. Alternately, you can configure the setting via the registry.
Registry edit

    * Click Start, type regedit.exe and press Enter
    * Navigate to the following branch:

    HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows \ CurrentVersion \ Policies \ System

    * Create a DWORD (32-bit) Value named HideFastUserSwitching
    * Set the Value data for HideFastUserSwitching to 1
    * Quit the Registry Editor.