automatic "join" for groups?

[cat_san]

going thru the documentation, i noticed that there was a blurb about profile fields being used for calculation? (or maybe that was giving a calculated value --- i'm not sure )...

what i want to do is fairly simple:
profile field called "gender" -- and the gender is either male or female.

i wanted to create a "men's" discussion and a "women's" discussion --
all the others can be for everyone....

but i only wanted to let the women in the "women's" one, and the men into the "men's" discussion.

is there a way to automatically join someone to either a "men's subgroup" or a "women's subgroup" in the registration.php file when the hit submit? ---
since i know i can restrict access to a forum based on subgroups -- or is there a way to restrict access to a discussion based upon a single profile field????

thanx in advance.