Creating my own mod -- need direction

Ok, I want to create a feature where when a user signs up, they will select from a drop-down menu showing a list of colleges.

That requires me to go to the admin->builder->join form (and create a selector).

Now, in the "Members" (browse.php), I want to remove the "Country list" and replace it with the selection of schools.

What files do I edit? Can anyone give me some details pointer?

Thanks for your effort.

I guess the next step is to figure out how to modify browse.php to display the list of schools?