The following KB articles have been released addressing what steps need to be taken for support of LCS 2005 SP1, OCS 2007 and OCS 2007 R2 in a Windows 2008 R2 domain, as well as installing OCS 2007 R2 on a Windows 2008 R2 member server:
One item to take note of. The following scenarios are currently not supported on a Windows Server 2008 R2 operating system:
For a quick reference of which domain controller OS versions support each version of OCS and which AD forest and domain functional levels are supported by each version of OCS, check out the following TechNet article:
One question: Can I install a brand new server with Windows 2008 R2 and install LCS 2005 SP1?
Is it compatible?
LCS 2005 was only supported on Windows 2003. It was not tested, and therefore wouldn't be supported.