I have now answered a couple of thread on http://silverlight.net about graphics in Silverlight and sprite animation this week. Therefore I thought I might also as well, post the same links here on my blog. Actually I think I have posted all of the links on my blog before, but here they are together in the same post.
Frame-based animation using clipping
For games, the typical animation style is "frame based" animations. This can been archived in Silverlight using "clipping". Bill Reiss over at Bluerosegames.com, have created a pretty good article about how to do this:
Principles of basic animation in Silverlight
At MIX09 Jeff Paries had a pretty good session about "Principles of basic animation in Silverlight". He shows different ways of doing animation and some basic physics (using vectors to simulate gravity)
Deep dive into Silverlight graphics
When doing graphic intensive stuff in Silverlight, like games, it's good to know something about how the graphics pipeline in Silverlight works. Seema Ramchandani had a good session about this at MIX09.
Hope this help you in the right direction