If you want to login as administrator account in Windows Vista, you can use the following steps.
1. Run the command prompt as an administrator.
2. Type the following command in command prompt.
net users administrator /active:yes
3. Then log off or switch user and you’ll see the administrator account in Vista Login.
If you want to hide the administrator account back, just type following command
net users administrator /active:no
Note : You can also use the same technique for other account name too. Use ” ” for the name contains white spaces.