Thank you for your post.
When you download the Business Productivity Kit, there are three folders: BPS_2.0, bps_graphics_pack, and bps_How_To_1.0.3. If you open the last folder, there is a PDF document that covers the entire solution and how it was built. It is not a tutorial for the system, but more of how to modify it for your own personal needs.
If you have specific questions about a module, let me know, and I'll dive into it with you.