Windows Vista UAC, User Account Control.

Most of us will never need to turn off(disable) the UAC security feature. In the event that you do need to turn off UAC(installing software, making certain Operating System changes etc), we recommend you enable the UAC security feature after the install or make changes.

Note: Enabling or Disabling UAC requires you to reboot your system.

To disable UAC, do the following:
Type "msconfig" in the Run From Start menu to open "System Configuration".
Click "Continue" at the UAC dialog prompt.
Select the "Tools" Tab in System Configuration.
Select the "Disable UAC" tool and click on the "Launch" button.
Restart the computer.

To enable UAC, do the following:
Type "msconfig" in the Run From Start menu to open "System Configuration".
Select the "Tools" Tab in System Configuration.
Select the "Enable UAC" tool and click on the "Launch" button.
Restart the computer.