The two methods given above did not work on my Vista Home Premium
system that was not an upgrade from XP. Because it was not an upgrade,
Local Users and Accounts was not available under Manage Your
Computer. And the last screen when clicking Advanced twice after
entering "control userpasswords2" at the Run prompt was stated as not
being available under Home Basic and Home Premium.
However, the following did work:
Enter "net user administrator /active:yes" at an elevated command
prompt window. Next time you log in, the Administrator account,
(initially WITHOUT a password) will be presented with an option.
To turn it back off, substitute "no" for "yes" in the command text.
For more information see "What happened to the Administrator
account",p 437 in the book, Windows Vista Inside Out by Bott,
Siechert, and Stinson.
KenF