Check out this step by step tutorial by Martin Krüger(SilverLaw) about how to make a ChildWindow rotate.
This day I read a question at the Expression Blend and Scetchflow Forum about how to make a ChildWindow rotate. Interesting enough to build a quick and simple solution for that, including a rotation when the ChildWindow opens. So here it is. You can view an example and download the sourcecode of a sample application at the Expression Gallery. The Sourcecode is Silverlight 3, but the implementation for Silverlight 4 is similar.
The following step by step tutorial builds a Silverlight 4 app.