Paco,
Sloan is also running 2.1 and on our system, site wide administrators can control folder permissions in any class or community because site wide admins have a button on the Documents pages that group admins don't: "modify permissions on this folder." Group administrators have the interface to control file-level permissions only. So what i have done for faculty is ask them create the folder they want to use, and then i go in and modify the permissions so that students can upload only.
Dee Kane
