A:
Yes, you can have a mix of Windows Server 2008 R2, Windows Server 2008, and Windows Server 2003 R2 in a single DFSR set. However, you need to apply a hot fix to the Windows Server 2003 R2 boxes to ensure proper functioning. Find this hot fix at the Microsoft support article, “DFSR fails from a computer that is running Windows Server 2008 R2 to a computer that is running Windows Server 2003 R2.”
Looking for additional troubleshooting assistance with Windows administration issues? See more of John Savill's FAQs for Windows.