adding unix groups

[JPOULIN%BOWDOIN.BITNET at mitvma.mit.edu]

I'm running ULTRIX 2.0 and I can't figure out how to add additional
groups to a user's account.  Some of our privaledged accounts belong
to 2 or 3 groups.  Also, does anyone know the name of the file that
lists who belongs in which groups?  I checked /etc/groups, but this
has been long outdated.  Anyone know of another standard file or is
this a local quirk?  ANY help would be *greatly* appreciated.

Jeff Poulin
jpoulin%bowdoin.bitnet at cunyvm.cuny.edu