The Microsoft Dynamics AX Sustained Engineering team announced the compatibility between the released versions of Microsoft Dynamics AX and Release Candidate of Windows 7 and Windows Server 2008 R2:

Windows 7 -=> Microsoft Dynamics AX 4.0 SP2 and Microsoft Dynamics AX 2009 RTM and SP1 (Supported as a client only, in 32 bits and 64 bits mode).
Windows Server 2008 R2 -=> Microsoft Dynamics AX 4.0 SP2 and Microsoft Dynamics AX 2009 RTM and SP1
Operating System Supported in 64 bits only.

The System Requirements of Microsoft Dynamics AX 4 and Microsoft Dynamics AX 2009 will be updated on Customer Source and Partner Source shortly.