A. Some special rules exist when you upgrade a back-end/front-end Exchange setup. You can't have an Exchange 2003 back-end server with Exchange 2000 front-end servers in one administrative group. You must upgrade all front-end servers to Exchange 2003 before you upgrade back-end servers within an administrative group. After you upgrade the Exchange 2000 front-end servers to Exchange 2003 or replace them with new Exchange 2003 front-end servers, you'll be able to upgrade the back-end servers to Exchange 2003. You can find more information about Exchange 2003 dependencies at http://support.microsoft.com/?kbid=822178 and http://support.microsoft.com/?kbid=822942.