If your Exchange 2003 server also acts as a domain controller, you've probably experienced problems with shutting down the system. The process can take a very long time, getting to the point where you might think that you'll have to forcefully shut down the server. And this problem can occur regardless of the quality or speed of the server hardware you're using.
What causes this behavior? The system shuts down the Active Directory services before stopping the Exchange services. The Exchange services then go through several attempts to contact the directory, even though the service has shut down.
Typically, the services will time out, allowing the system to shut down and reboot. In some cases, however, the system appears to hang, requiring manual intervention to recover.
The workaround in this case is simple. Stop the Exchange services before shutting down the server. Because the directory services will still be running, the Exchange services will shut down normally. The system will then reboot much faster, with no risk of hanging.