The Configuration Manager product team recently announced some changes in what's officially supported in ConfigMgr 2007, including SP1, SP2 and R2. Here’s one big App-V 4.6 related change here:
Microsoft Application Virtualization 4.6 is now supported on ConfigMgr 2007 R2 with ConfigMgr 2007 SP2 – System Center Configuration Manager 2007 R2 with System Center Configuration Manager 2007 SP2 now supports Microsoft Application Virtualization 4.6 Desktop Client and Client for Remote Desktop Services. This client release enables support for Windows 7 and Windows Server 2008 R2 and support for 64-bit operating systems. No software updates are required.
Windows Fundamentals for Legacy PCs SP3 is now supported on ConfigMgr 2007 SP2 – System Center Configuration Manager 2007 SP2 now supports Windows Fundamentals for Legacy PCs SP3 as a client platform.
More info: TechNet blog