The organization chart control is their own, this is the whole point of the demo page.
The user interface elements are fairly simple rectangular elements. The real trick is calculating their placement on the panel and routing the trunk.
I guess the missing piece of the puzzle is what we usually call it. If you know that then you have the basis for searching the Internet for algorithms in order to do such things in both academic and some other product, and then bring this knowledge into your own Silverlight code.
Alternatively, you can simply buy the product.