General help

We at UCLA developed a solution for this called "Public/Private". It is a patch that you apply to Moodle.

You can find the patch here:

http://moodle.org/mod/data/view.php?d=13&rid=2768

Basically, all students that get enrolled in a course that has Public/Private enabled join a group called "course memebers". That group is part of a grouping called "Private Course Material".

With those two things in place, anyone with teacher privledges or higher can click a lock icon on any resource or activity to either open up that item to guests, and others not enrolled, or lock it down to only members of the course.