From the Class Designer team blog:
We’ve published a set of set of add-ins which augments existing functionality in the Visual Studio 2005 Class Designer and the Distributed Systems Designers. The Design Tools Enhancements add-in provides a common set of features that can be used by both the Class Designer and the Distributed System Designers, such as pan/zoom window and rich formatting commands. The Class Designer Enhancements add-in provides additional functionality for the Visual Studio 2005 Class Designer, such as HTML export and nested type creation commands. This download includes all necessary source code and a Visual Studio project template for creating your own add-ins for the Visual Studio 2005 designers.