Windows Server 2003 R2 is just CD2, Keep that in mind when time comes for adprep
I’ve seen a few posts that people have tried to run adprep to install Windows Server 2003 R2 on there domain controllers and failed. That’s because they have lunched adprep from CD1 that’s only contains Windows Server 2003 SP1. The Windows Server 2003 R2 is placed on the CD2. So make sure you run adprep from CD2 if you planning to upgrade your Domain Controllers to R2 or just want to take use of te features in R2 that requires the new schema updates.
Extending Your Active Directory Schema in Windows Server 2003 R2
The schema defines objects and attributes and the types of data they can store for Active Directory. You can extend the schema to support new operating system features and applications, or to add RFC-defined attributes that are commonly found in other Lightweight Directory Access Protocol (LDAP) directories. You might also extend the schema so that the directory can store information that is interesting to your organization.
Extending the schema for a new operating system version is a two-phase operation that consists of a one-time schema extension on the domain controller that hosts schema operations master role (an operations master is also known as flexible single master operations or FSMO), and a one-time update on the domain controller that holds infrastructure master role in each domain in the forest. Both operations are performed with the ADPREP tool located on Windows Server 2003 R2 Disc 2.
These topics focus on using the adprep /forestprep command to add the Windows Sever 2003 R2 schema extensions that are required to support the following Windows Server 2003 R2 features or server roles:
* Distributed File System (DFS) Replication Service
* Domain controllers running Windows Server 2003 R2
* Identity Management for UNIX
* The Deployed Printers functionality of the Print Management console
These schema additions are automatically installed when you use Windows Server 2003 R2 installation media to create the first domain controller in a new Active Directory forest. However, if you are planning to add a domain controller that runs Windows Server 2003 R2 to an existing forest, you must extend the schema first. The following topics explain the Windows Server 2003 R2 schema update, interoperability considerations for x86-based versions and x64-based versions of Windows Server 2003 R2, and the steps for extending the schema
This KB article is very helpful.