Letting user select primary group ID at logon in ksh

[mardigras]

Want to let users set their primary group ID at logon. All accounts are set up in ksh and therefore have a .profile. The users are all CADDS designers and are fundamentally UNIX illiterate. Currently trying from within the user's .profile to invoke an Xterm window running a script to list the groups of which the user is a member, let him select his default group, and then run the "newgrp" command.
No success yet.