Custom User Fields, Preferably Asked For During Registration—

I have distinct pieces of information Id like to capture from users, preferably during registration. I have seen only one registration add on plugin, but it looks like all it does it force users to answer user fields that are already part of the user profile (AIM screen name, etc). I am building a political website for my state and would like to ask users what congressional district they are a part of etc- How do I add additional user fields to a user profile page and how do I make answering these questions part of the registration process?

Any help is GREATLY appreciated!