Is there a CONF file for groups???

[Tom H]

> I have set up a server with Karmic and about 30 users, each of which belongs
> to group "students." This group is their primary and only group. The problem
> is that they cannot log into the system! Not locally, not via ssh, not via
> samba. It would appear that new groups do not have, by default, logon
> privilege. Does anybody know of a conf file that would give specific
> privileges (such as access to the system) to a group?

Is the GID of students below 1000?