First goto the 2k pdc and run srvmgr from the start menu. Create a new Windows NT Backup Domain Controller in server manager, for the computer name, put the computer name of the BDC you are going to install. Go back to the NT server and install Windows NT 4 and a BDC connected to the network. After this is done on the NT machine open server manager and synchronize the NT machine with PDC and after this is done disconnect from the network and promote it to a PDC with server manager.