I wrote a tutorial about a general solution to make a regular Silverlight 3 and 4 ChildWindow rotate. Quite straight forward. Additionally to the sourcecode of the contribution at the Expression Gallery the tutorial describes a reliable technique how to add a rotation at the Open procedure of a ChildWindow - ChildWindow.Show() -. This technique gives the opportunity to add every animation of your choice to the open procedure of a ChildWindow and therefore provides a solution to in full customize the open procedure.
Have fun!
Martin (LawBot / SilverLaw)