w2k primary domain controller crashed

administer a network with 2 W2K server domain controllers, one acted like a PDC and the other has Exchange 5.5, the PDC crashed, the exchange has active directory, no DNS installed, would like to reinstall the crashed PDC with W2k server with activedirectory and DNS, how will this affect the cuurent setup with exchange and active directory. If I understand W2k correctly there is no promoting domain controllers to primary like in NT 4, how do you add a PDC to this setup?