I am not an unix guru, but I have found the answer to the question of:

how to run gwm instead of twm.

You need to edit a file called xinitrc.  I believe it was in /usr/lib/X11/xinit

Change the line at the end from twm to gwm.  Gwm has a mwm emulation mode
that I think looks great, but I can't get the menus to pop-up.
mark@student.business.uwo.ca (Mark Bramwell CS STAFF)
Western Business School  --  London, Ontario