When you attempt the subject upgrade, you receive:

Certificate Server 1.0 cannot be upgraded directly from Windows NT 4.0 to Windows Server 2003.
If you continue, your Certificate Server settings may not be saved, and Certificate Server may be automatically uninstalled. If you upgrade first to Windows 2000 and then upgrade to Windows Server 2003, all your Certificate Server settings will be preserved.
For more information about Windows Server 2003 Certificate Services, see the Microsoft Web site.

The only way to upgrade a computer that is running Windows NT 4.0 Certificate Services to Windows Server 2003 is to first upgrade it to Windows 2000 Server. Then upgrade Windows 2000 Server to Windows Server 2003.