OSX: Setting permissions and ACLs
Nice article about how to setup Permissions and Access Control Lists (ACL – i.e. permissions on steroids ;-)) in OSX.
Another article from Ars Technica (although specifically about 10.4 Tiger, things should not be that different in 10.5 Leopard – it’s UNIX after all).
And a some what related article about File Sharing in OSX can be found here.