Our Exchange organization has both Exchange 2000 Server and Exchange Server 5.5 servers. We use the Active Directory Connector (ADC) to synchronize directories between AD and Exchange 5.5. Will we need to upgrade the ADC to support Exchange Server 2003?

Absolutely. In fact, if you try to install Exchange 2003, the Exchange Setup program will tell you that you first must upgrade the ADC to the Exchange 2003 version.