So Philipp asked. Now its here.
DFS-N is DFS Namespaces. It's available in Windows Server 2003 Standard SP1 and up to Datacenter. Windows Server 2003 R2 Standard through the Datacenter adds a new and much better management UI to it but essentially the underlying functionality was provided Windows Server 2003 SP1. This is the failover/failback support, Site affinity and targetting services based on sites etc.
DFS-R is the really cool bit. This replaces FRS for file replication only (SYSVOL support will be added in the Longhorn server timeframe - dont try it yet! You will kill your AD!). This technology is available in Windows Server 2003 R2 Standard through to Datacenter. It implements the block mode replication functionality and Remote Differential Compression (RDC).
The management UI works with both of these to create linkages between the two but you dont necessarily have to implement them both together - they can be mutually exclusive if you want. The other usual questions I get is around AD dependencies. While we're saying that in order for it to fully work you need to have Windows Server 2003 SP1 on all your domain controllers, parts of it do work in a Windows Server 2003 or even Windows 2000 AD forests. You need to have extended the schema though with Windows Server 2003 SP1 extensions though. The tradeoff is some functionality loss. If you arent using Windows Server 2003 SP1 DC's then client failover/failback wont work and the site based targetting wont work either in DFS-N. E
For DFS-R/RDC functions, each end obviously needs to have Windows Server 2003 R2 for DFS-R to work. You cant just have one end with DFS-R and the other a standard Windows Server 2000/2003 box.
So to answer your question Philipp, the main bits are available in Windows Server 2003 R2 Standard aswell.
BTW - theres a new blog that just started called The Filing Cabinet and is dedicated to the filing system and replication technologies in Windows...check it out!