Here is a couple of examples by Petzold:
Let There Be Shadows
Let There Be Shadows (Part II)
You may find the WPF3D Team Blog
] to be of some interest.
The XAML Exporter for Blender
] allows you to export to xaml from blender
] - there are limitations on it's abilities to deal with lights and shadow, among other things, but if what you want is reasonably simple, it will do.
While it's possible to do a lot of 3d stuff in xaml - XNA
] offers a more efficient programming model.