The Microsoft WEB link below highlight the various levels of compatibility with existing Microsoft server products and Windows Server 2003. While some products require a service pack to run directly on Windows Server 2003, it should be noted that all Microsoft Server products will run within a server environment that contains Windows Server 2003 servers. Windows Server 2003 will be able to coexist in environments with previous versions of Windows servers and the applications that run on top of them. By introducing Windows Server 2003 into those environments, customers will be able to take advantage of the new features and security enhancements. Windows Server 2003 has been designed to work in mixed environments with previous versions of Windows server. You can continue to run your applications that do not have an upgrade path in environments with Windows Server 2003 machines.