Just a quick tip that you do not need to have your entire RDS environment at the Windows Server 2008 R2 level to be able to utilize the nice integration features of RemoteApps in Windows 7. I am referring to the feature of subscribing to a feed of applications and thereby have a dynamic publishing of RemoteApps for the ends users, in the users start menu.

To get this working all you need is a Windows Server 2008 R2 to host the RDS Web Access role, which then can include and publish RemoteApp sources that are based on Windows Server 2008 hosts (no R2 requirements there).