The administrator account let you install any program or change any on windows vista setting

Note: any change you made with the administrator account will affect in all other users account
so you have to be careful for what you changing

To add the administrator account to vista welcome screen

start/ run/ type control userpasswords2

under the user account window select the advanced tab

click on the advanced tab under advanced user management

From Local user and grump window select users then double click on the Administrator

in the Administrator properties uncheck Account is disabled

then click ok
reboot you pc or log off the current user you will see the administrator account in the welcome screen