Auto permissions for forum based on profile field

[criscokid]

I'm planning on creating a few 'hidden forums' that only registered users will have access to. The thing is I want new users to have automatic access / permission to those forums when they sign but based on a profile field. How do I go about doing this?

As an example: If the profile field for gender is male then that user gets access to the 'male forum'. If the profile field for gender is femal then that user gets access to the 'female forum'.

The profile fields I'm thinking of using make use of drop down lists so the text inn that field is always exactly the same.