Teaching with Moodle

We're currently building a site (Moodle 1.7) where the owner wants progression limited to having attained a certain grade before the student can move on to the next "section/topic" of the course.
OK, I know we can do that by using the Lesson module but the Lesson module does have some inhibiting "non-functionability" e.g. limited quiz capabilities, uploading an assignment for marking etc.
Does any one have any idea how we could structure a course using such activities/resources as assignments, Hot Potatoes, Scorm etc and still be able to restrict progress to a grade mark within a topic.

Hope this is the right Forum. If not please point the way!

Dave