[Samba] Changing a user's primary GID

[Wong, G. MR EECS]

I'm using samba version 3.0.10 on an Intel PC running Redhat Linux 3.0
AS.  I am using winbind with the idmap_rid module to authenticate users
to Windows AD.  All the current Linux user account names are exactly the
same as the corresponding Windows AD SAM acct names.  Everything works
beautifully EXCEPT for the GIDs generated from the from the AD Groups
that the Windows accounts belong to.  (The UIDs are NOT a problem.)  It
seems like they all belong to the same group of "Domain Users".

This is what I DO NOT want!  At a minimum I need to have users in one of
2 Linux groups - as their primary group - a faculty or a student group
since our current utility programs use Linux group permissions to work
properly.  A student account can easily be determined from the
SAMaccountName - if it starts with a lowercase "x".  If not it is a
faculty account.

I DO NOT control the info in the Windows AD system.

Is there a way to force a user be put into a particular (LOCAL) Linux
group when logging into a Linux host running Samba winbind.  This would
be there primary group while logged in.
I really have no use for the domain group.

Is there a utility or would the code have to be hacked?  If the latter
is true what C programs need to be modified?