For each user account in a user forest, you must create a corresponding disabled user account in the resource forest. This process varies depending on whether or not Microsoft Exchange Server is deployed in your resource topology.
If Exchange Server is deployed in your resource forest, the disabled user accounts will already exist and many of the necessary attributes on the disabled user accounts will be populated. You can run a script to update the attributes that are not automatically updated by Exchange Server.
If you do not have Exchange Server deployed in your resource topology, then you must create the disabled accounts and manually copy the required attributes from the user accounts in each user forest to the corresponding disabled user account in the resource forest. This method can introduce problems that are difficult to fix. As an alternative, consider deploying Office Communications Server in the central forest topology. For more information, see Deploying Office Communications Server 2007 R2 in a Central Forest Topology.