Is there a mechanism for creating a "book" with daughter pages of varying types? I've installed the CCK to allow customization of my content types. I'm attempting a collaborative curriculum design site, and here's what I'd like in terms of hierarchy:

GRADE - the top level page, with links to all units in grade
UNIT - the main page for each unit, with merely a general description, and links to all daughter lesson pages
LESSON - fields for teaching idea, textbook pages, and links to daughter components pages
COMPONENTS - activities, labs, games, experiments, stories, etc. The details of each piece of a lesson.
COMMENTS - final step is to provide comments on each component from a community of users, and the ability to add new components to the curriculum.

So far, I can only make a book of SAME content type (which means I can't create custom fields for each of my desired content types like GRADE, UNIT, LESSON, etc...) Is there a way to link content of differing content types into a single book?