The installation is straightforward once you understand the concepts.  Partial DFS functionality is already installed on Windows Server 2003.  The replication side of things needs to be installed separately.  As long as you have upgraded to Windows Server 2003 R2 you can install this from Add/Remove programs and the Distributed File System category.  I recommend installing all 3 optional features as the extra management tools are better for managing your redundant DFS system.  This needs to be installed on the servers hosting the namespaces and the folder targets if you will use replication.

The extra replication features of R2 do require Active Directory changes.  If you have already upgraded your domain controllers to R2, then no additional action is required.  If you have not upgraded your domain controller to R2, no worries, you are not required to do so, but you do need to extend the schema.  Here is a link on how to do that.

Like anything of this nature, make sure to have a good disaster recovery plan in place and do this at a non-peak time.  However, the schema installation is straightforward and does not cause any interruption of service in Active Directory.

Once installed, three hot fixes should be installed, located here.  One is required for the client failback feature to fail back to the primary content server when it is back online after a failure, another allows you to have multiple domain-based DFS namespaces on Windows Server 2003 Standard Edition if you desire, and the 3rd supposedly fixes a potential RPC issue with replication (although I did not run into this issue). KB Article 898900 needs to be installed on all of the servers accessing DFS (the web nodes). The other two need to be installed on the DFS content servers.