groups

I want to store some files on a Macintosh (OS 10.2). They should be in the Public folder, but only accessible (= only readable) by certain people. Thus I would like to create a new group that has accession rights to these files. Strangely, the group command doesn't exist on MacOS X (chgrp does exist though). I downloaded the User Manager application. But the version for OS 10.2 was not really easy to use. Thus I used the NetInfo Manager.