I can tell you SQL Server 2000/2005/2008 are compatible with AD2008. R2 doesn't fundamentally change authentication mechanisms, so far as I am aware. So all 3 supported versions should still be fully compatible. Keep in mind that SQL Server actually hands off Windows authentication to the SSPI of the OS on which it is installed. And I've seen no guidance that Windows 2000 on up are not supported on Windows 2008 AD (other than the fact that Windows 2000 is coming to end of extended support).
K. Brian Kelley