So testing is complete and we now support Windows 2008 R2 for deployment with OCS 2007 R2. There are some scenarios that aren’t supported for Windows 2008 R2:
1. OCS 2007 R2 Group Chat won’t function in a Windows 2008 R2 forest or when GC member server are joined to R2 domain.
2. Group Chat on a Windows 2008 R2 server isn’t supported.
3. Upgrading the OS to Windows 2008 R2 for existing OCS installs isn’t supported.
4. R2 admin tools will on install in native 32bit or native 64 bit mode.
5. Development with R2 Speech server isn’t supported on Windows 2008 R2.
More info can be found here.