[fw-auth] Help with multiple roles

I'm trying to figure out the best mechanism for setting up Zend_Acl
for a "News" web app. Currently I have several departments (50+) and
several users (1000+). A user can be a member of one or more
department. There are three departmental roles; author, editor, and
administrator and one generic "super user" role. Now here is the
tricky part, a user can be an author for one department but an editor
for another department, and if they are a departmental administrator,
they inherit both author and editor permission as well as have the
ability to add users to their department or change the roles of
current users. Also, if you are a departmental administrator, editor,
or author, then you can ONLY manage news stories related to your
department. And of course there is the super user that can add
departmental administrators. How would you recommend I set up Zend_Acl
under this scenario? Please let me know if you need more information,
given this is my first post and I'm new to Zend Framework, please go
easy on me ;-)

Thank you,
Henry