If you've messed with the DWM API for Vista you'll have already realized that it kinda sucks. There's only an API for creating live 2D thumbnails on hWnds. The DWM actually renders all Windows to Direct3D textures. If we had access to these textures, we'd be able to do some pretty wicked things with the desktop. Sadly these API calls are locked away from us and we can only gaze upon what Vista "could have been" via Flip3D.
I have been trying to hack away at the DWM API(dwmapi.dll) and I believe I have made some progress. I am able to get the Direct3D texture for and hWnd and use it within a Direct3D application. The problem is I seem to only be able to get hWnds that are using 3D, so GDI redirected windows render black.
Here is a video of my progress. It's not anything visually jaw dropping, but it shows one application rendering another application as a texture on a 3D surface...all through DWM!
Video linked below.
DWM Hack Video