This article on how to use Visual State Manager is an edited version of a a section of a chapter David Kelley wrote for the book 'Professional Silverlight 4'.
Source: Hacking Silverlight
Part of the job of the designer or creative that you typically see being done in Expression Blend is skinning and templating controls, views, and other objects. For the most part, all controls have built-in templates, and in Visual Studio it is very difficult to get at these as they are part of the framework and not exposed. Expression Blend has a great tool to help you get at the templates by creating copies of templates for any control, putting them into your code and allowing you to edit them in the Designer using the Visual State Manager area labeled States that was mentioned earlier.