Carlosmcse-
Hello there... i had to do this exact same thing a few months ago for one of my clients. In a nutshell ... you need to do the following...
1. Join the new exchange server to the exchange organization
2. Move the mailboxes
3. Verify public folders, schedule free/busy, recipient update, routing master are controlled by new exchange server
4. Join new 2003 standard server as DC, make the new server (AD and File) a global catalog.
5. Make sure DNS has replicated, DHCP settings have been noted, any replication has taken place between the two domain controllers, all data has been copied off.
6. Once completely verified that you no longer need the SBS server, completely shut it off. You CANNOT gracefully demote this SBS server. YOU CAN NEVER TURN THIS SERVER LIVE ON YOUR NETWORK AGAIN
7. Seize the FSMO roles on the 2003 standard DC from the SBS server.
8. Run DCDiag to make sure all the roles are squared away and pass their respective tests
9. Run ADSIEDIT and navigate to the Configuration > Services > Microsoft Exchange > CN=<Name of your Exchange Org> > Administrative Groups > First Administrative Group > Servers and DELETE the recently powered off SBS server object.
10. Run NTDSUTIL /METADATA CLEANUP from the 2003 standard box and remove all instances of the SBS server.
11. At this point, DNS should have been replicated ... so all you should need to do is configure DHCP as it was on the SBS server and whatever other components you utilized on the old SBS server.
From this point... when you moved the mailboxes to the new exchange server within the organization... it SHOULD have automatically changed the Outlook clients to reflect the new server. Hope this helped.... please feel free to ask if you have any other questions. SBS to Standard domain / exchange migrations are pretty tricky and can go horribly wrong so please ask if you arent sure.
Chris Clancy, EnCE,CCE
" ... when you can't figure out what the problem is, find out what it isn't.... "