hmz.. in windows you can replicate to a slave, then promote that slave to a master..
*in theory* you should be able to sync with a zentian server, and then remove the NT box from the domain, setting then zenty as a master, but be carefull though, windows security might be in the way, i advise you to google first an amount of information, and tutorials and such (and keep your NT box at hand in case it fails)