Exchange 2003 – What’s new?
Exchange 2003, like many of the Microsoft’s 2003 family, is really just a point upgrade over Exchange 2003, e.g. Version 5.0 –> version 5.1. (This version was formerly code-named Titanium.)
The key new features are:
Because of their similarity, an upgrade from Exchange 2000 will be easy. All you really need is service pack 3 for Windows 2000 alternatively use Windows Server 2003 for Active Directory.
Where possible I like to keep systems in synch so I recommend either:
1) Windows 2000, Exchange 2000, Outlook 2000
2) Windows Server 2003, Exchange 2003 and Outlook 2003 (v 11)
My feeling is that not many people will migrate from Exchange 2000 to Exchange 2003, but those who have not yet migrated from Exchange 5.5, will go straight to Exchange 2003.
For much more on Exchange 2003 see here