Autodesk has just recently posted new White Papers on the CUI and Dynamic Block features found in AutoCAD 2006.
Customizing the User Interface Through the CUI Editor
The CUI White Paper covers how to create a command and then work with many of the different user interface elements that are available in AutoCAD.
Part 3: Advanced Features of Dynamic Blocks (written by Ellen Finkelstein)
The third part in the Dynamic Block series focuses on some of the more advanced topics like Cycling Insertion Points, Chaining Parameters and Visibility States.
To download these and other new White Papers visit the AutoCAD 2006 section of the Autodesk website.