1- Upgrade to 2008 R2 Domain - Preupgrade Tasks
Preupgrade Tasks- Transitioning / Migration/ Upgrading from 2003 to a 2008 R2 domain:
1. Make sure that SP2 are installed on all 2003 DC's.
2. Make sure Domain functional level is Windows 2000 native or higher.
3. Make sure you are using an account with the proper permissions.
4. Make sure the DNS is setup as an AD integrated DNS zone.
5. Make sure Exchange Server is updated with the currect SP level.
6. Make sure you backup Active Directory.
7. Make sure the Antivirus and FW are off.