Mac OS 9 multiple users can use the Mac Managers Database the runs on Mac OS X Server to verify users.
I've used Mac Manager and I've used Mac OS 9 but not together but I suspect they work together quite well.
Mac Manager isn't very mature but it is pretty powerful and simple to set up. You set everything up from a Mac OS GUI. You make users have full finder, limited finder, or Panels. You can limit users access to certain applications, access to removeable media, limit which printers they can use, and you can give disk quotas.