The Setup Assistant gives these examples when it asks you to enter a hostname:
server.example.com
www.example.com
This is the correct form for a hostname in Mac OS X Server 10.3, and it's the form that will be listed for the HOSTNAME in the "/etc/hostconfig" file on a properly configured server.
If you need to change the hostname later, you can use the "changeip" command in Terminal. To learn more about the command, see the
Mac OS X Server Command-Line Administration Guide or type "man changeip" in Terminal.