I saw some good tutorials about this on moodletuts that you can check out. I`m also trying to implement some on http://www.frivboom.com but still working on this . Hope this helps.
Thanks for the link, I had a look at moodletuts but unfortunately not what im looking for. I think I may need to look into modifying the moodle core to build in this functionality as I cant see any other way to manage my users.
the user hierarchy is an ideal requirement, but with that I need to enrol people on courses based on groups, but also hide/unhide courses (or course categories) based on their group membership