I have no Idea what your Budget is. But I Built a New Server 2003 Server and Then loaded Exchange 2003 Enterprise. Then moved the Mailboxes through Active directory. Easy as pie with Two Servers. Then We I decomisioned all my Exchange 2000 I promoted my Exchange 2003 to Native mode. I am not sure if you will have a problem setting up Exchange 2003 Standard next to your Exchange 2000 Enterprise. Check with Microsoft, but I think it is all compatable. The New Exchange server should just add right in and Active Directory should still move Mailboxes.