Have you been trying to create drill-down charts with the Silverlight Toolkit? If so, I have created an approx. 7 minute video for internet.com which demonstrates the basics. The video can be seen here. The code I created for this video can be downloaded from here.
If you would like to learn how to begin using the Chart control in the Silverlight Toolkit, I encourage you to review my two previous posts: Introducing the Chart Control and Getting Started with the Charting Control.
I hope this helps you get running with this powerful control.