If you have a Domain and Forest functional level of 2008 you should be able to create DFS Namespaces that are enabled for Windows 2008 mode. However when creating a DFS I noticed that this option was greyed out. I checked again in Active Directory to confirm the Forest and Domain was running at a 2008 Functional Level and it was. It turns out that this option to enable Windows Server 2008 Mode does not appear until the DFS Namesspace service and the DFS Replication Service have been restarted on the Namespace server and the Domain Controller that holds the Operations Master FSMO role.
After restarting these services try and create a new namespace and the option to Enable Windows Server 2008 Mode should be availible.