With the 3D Tools for the Windows Presentation Foundation library, which is now available on CodePlex, the Windows Presentation Foundation team has reduced the 3D case back to 2D, and made it possible to interact with 2D objects within a 3D scene. See the WPF 3D Team blog for more details, samples, and all the links you need.
You may be interested in the Channel 9 video on this toolkit, which is introduced like this:
One of the really cool features of WPF is being able to take any 2D user interface and easily place it on a 3D surface. The most common request after doing this is then having the ability to interact with this 2D content on the 3D object. V1 of WPF doesn’t have this feature built in, but with some extra code, this feature can be built on top of the product.