The problem you are experiencing is because Exchange 2003 doesn't work on Windows 2008.
From 'The Exchange Team' on Technet:
Exchange 2003 Service Pack 2 will be similarly supported: Exchange 2003 cannot be installed on Windows Server 2008, but will be supported with Windows Server 2008 domain controllers.
From MS KB948680 Description of the Microsoft server applications that are supported on Windows Server 2008 (Under "Applications that are incompatible"):
- Microsoft Exchange Server 2003