Moving from exchange 2003 to 2007 within the same forest is very easy. Let me break down the main steps that you need to consider in the transition.
1. There is no in-place upgrade from 2003 to 2007. You need a new 64bit server.
2. Exchange should be in native mode, no pre-2000 exchange in the environment.
3. Schema Master and GCs should run atleast Windows 2003 SP1 or higher.
4. Extend the schema if it is a large organization, otherwise run the exchange setup and it will do it
5. A routing group connector for 2003 – 07 mail flow is created during the exchange setup.
6. Replicate public folders from 2003 to 2007 either manually or using the scripts in the 2007
exchange installation folder.
7. Replication for Schedule+Free/Busy and OAB is set automatically during the exchange setup
and hence doesn’t have to be touched.
8. Repoint client access (owa, activesync, outlook anywhere) to the 2007 server. Mailboxes on
2003 server can be accessed using OWA 2007, as the request will be redirected.
9. Move the mailboxes from 2003 to 07 either using the move-mailbox cmdlet or EMC.
10. Once all the mailboxes have been moved to 2007 server, configure send and receive connectors so that mail flows in and out through the new server.
11. Delete the smtp connector for 2003 – 07 communication, which was configured during the
12. Repoint RUS to 2007 server and uninstall exchange 2003 from add/remove programs.
Make sure you have access to exchange 2003 cd or installation files during the removal
That is it, in a nutshell.