UPromote is the only software utility that can promote your NT server to a NT domain controller without re-installing the operating system.

When you installed Windows NT Server, you were asked if you wanted to create a a domain controller (DC). Your choice was permanent. If you declined, you could never create one later (Q193219).
With UPromote you can
A domain controller puts all of your passwords in a central database. When a user logs on to a desktop PC, it consults the domain controller to verify your password.
A small organization starts with a workgroup, a collection of machines that can share files and a printer. A domain is a larger collection of computers where access to files and printers is controlled by the domain controller. A domain has exactly one primary domain controller and optionally one or more backup domain controllers.
Only UPromote can rescue you from a difficult dilemma: You need a DC but you already installed Windows NT Server without it. What do you do? Do you waste days of downtime while you re-install everything, or do you spend thousands of dollars on another computer?
You can move your BDC to a new domain with a simple 2-step procedure.
You can use the same 2-step procedure to move a NT 4 BDC into a Active Directory mixed-mode domain.
You can demote a NT server to a regular standalone server. After you demote the server you can re-join it back to the domain as a member server. It will continue to use the same domain accounts that it used before.
Active Directory allows you to run a mixture of NT BDCs and Windows 2000/2003 servers. This is called "mixed" mode. To run in "native" mode all domain controllers must be running Windows 2000/2003. You cannot switch to native mode if any NT BDCs remain in your network.
It takes only a few minutes to use UPromote to downgrade your last NT BDC domain controller to a standalone server. After you demote the server, you can re-join it back to the Active Directory domain as a member server. You can then upgrade your AD domain to native mode and enjoy the full benefits of Active Directory.
UPromote works by updating the system registry. To create a PDC it converts all local user accounts to global user accounts. To create a BDC it copies the user accounts from the PDC and then synchronizes the Security Identifier (SID) to match the PDC. To create a standalone server it converts all global user accounts to local user accounts. It does not modify any EXE or DLL files.
For technical details see UPromote Operation.
UPromote has been thoroughly tested and is safe to use. The result is indistinguishable from a domain controller created using the Microsoft setup procedure. As an added precaution, it backs up your entire registry. This allows for easy recovery.
Any domain controller created with UPromote can be safely upgraded to Windows 2000 Server or Windows Server 2003.
UPromote has been used to promote/demote NT servers at hundreds of businesses and colleges, including many Fortune 500 companies.
For more information, see the list of Frequently Asked Questions about UPromote: