I'm assuming that they are on two differnt IP subnets...I have in the past confgured WINS on both subnets and then configured PUSH/PULL for WINS. That way information about domain controllers and that could be shared between the subnets. If this is not an option than I would recommend a LMHOST files on the Domain Controllers that have the Server names preloaded and defined as the file specifies. The instructions could be found in the files itself. Do a search for the file and you want the one in the etc folder. Also if you make any changes to this file it has an extension of SAM. Make sure you take that off. The file should have no extension.
Good Luck!