How to LINK a Silverlight library to the files of a normal Class Library

Answer 1

You need to "add an existing item" to you silverlight library. Instead of simply clicking "add", click on the arrow on the side of the add button and choose "add as link". That will create a "shortcut" from the original file to your silverlight library.

Obviously you need to make sure your class does not make use of anything not in the silverlight BCL.