Supportability is available for Office Communications Server 2007 R2 member server role on a Windows Server 2008 R2 operating system
This article describes the supportability for the Microsoft Office Communications Server 2007 R2 member server role on a server that has a Windows Server 2008 R2 operating system installed. However, the following scenarios are currently not supported on a Windows Server 2008 R2 operating system:
- Upgrading the operating system to Windows Server 2008 R2 for an existing installation of Office Communications Server 2007 R2 is not supported.
- Deploying Microsoft Office Communications Server 2007 R2, Group Chat on a Windows 2008 R2 operating system or in a Windows 2008 R2 domain is not supported
- Office Communications Server 2007 R2 administration tools will only be installed in native 32-bit mode or a native 64-bit mode. Because of an application compatibility issue with Windows Server 2008 R2, installing Office Communications Server 2007 R2 administration tools in 32-bit mode on a 64-bit Windows 2008 R2 operating system is not supported.
Read more http://support.microsoft.com/default.aspx/kb/982021?p=1