We have CentOS 5.5 server running samba. A bunch of macs are connecting to it and accessing shares. All the samba users also have real accounts. There is a group admin who have full rights to everything (so I think). I've added all the users to the admin group.
When a user creates a new directory within the file tree, only he or she can access it. We need it so when a user creates anything new, all the other users with rights to the share have access to it.