Members joining forum

Let me tell you how I have a forum setup.  I have a forum set where I have 2 different groups I have setup the groups where 2 stars can view one forum and 3 stars can view another. but both can not view each others.  This is a city forum where we let groups use the forum for there use only.  ie girl and boy scouts is hidden too all but admin and 2 stars then I put a password so each group can not be read by others.

Currently I have to ask them to join then email me there username so I can change there rating.  I was wondering if there is away a person can join the forum system and choose what group they need to be part of.  I am sure this would have to be a custom login page.

I guess this would be more of a custom newbie setup.