Use the Code: WRAC11
Wow, check out this sample of a 3-D realtime engine. This is just freaking awesome!
http://babylontoolkit.codeplex.com/
Download this immediately, that is if you are experimenting with Silverlight 5. Otherwise, ignore it!
It contains (and I cut and pasted this from the link above in case you missed it):
Babylon Toolkit provides a complete toolbox for Silverlight 5 3D. It includes: