How can I properly remove a BDC from a Windows NT 4.0 domain?
You need to shut down the BDC and use the Server Manager to remove the BDC's computer account from your NT domain. Open the Server Manager at your PDC, select the BDC's computer account, then select Remove from Domain from the Computer menu.
To make sure that this change is quickly replicated to all other domain controllers (DCs) in your domain, in the PDC's Server Manager, select the PDC's computer account, then select Synchronize Entire Domain from the Computer menu.
Finally, from the Server Manager, remove the BDC from your DC's directory replication configuration by selecting the appropriate DC account and double-clicking to open its properties. Click Replication and remove all occurrences of the BDC's computer account.