When you install Vista (in any flavor: 32/64-bit, home, business, ultimate or enterprise), the first account that is created gets put into the local Administrators group; subsequently added accounts are created as limited users unless otherwise specified.
This leaves for an amusing little scenario (not):
- Install Vista
- Add machine to a Domain
- Log in to Vista using a Domain Admin account (giving administrative privileges on the machine)
- Delete the (admin) user created during install
- Dis-join from the Domain
Luckily, the folks on the Vista team recognized this possibility. The fix is to restart in Safe Mode (hold down F8 during POST). Vista will boot into the Safe Mode GUI using the built-in Administrator account, even though it is disabled. From there, you can enable the Administrator account, reboot, then log in "normally" to re-join the domain.
You can also shorten the process by using "Safe Mode with Networking" to re-join the domain (whether you enable the Administrator account or not).
If you enable the local Administrator account using this process, it does remain enabled, even after rejoining the domain.