To enable the hidden windows vista administrator account follow the steps.

1. Open a command prompt as Adminisrator this can be done by using the right click menu "Run as Administrator" (or use CTRL_SHIFT+Enter in the search box)
2. Type the following command
   net user administrator /active:yes
3. Logout and see the Administrator account in the welcome screen.

To revert back or to disable the administrator account issue the following common in the same scenario

net user administrator /active:no