Users In Multiple Groups

[El Alcahuete]

When a Workgroup manager user is a member of multiple groups, is there anyway to make it automatically log in to one of those groups on a normal basis as if it was the only group, however still have the option to log into the other group if desired?

I thought that was an option at the login screen, however when I hold down the option key it doesnt do anything.

Thanks.

Xserve g4, Mac OS X 10.4 Tiger, Panther on all user machines