Adding to profile.php

I'd like to add a column to the users table that will indicate whether a user is or isn't willing to receive a newsletter from my site.

To that end I want to add another section to the profile.php page, under 'essentials' that allows the user to select whether or not to receive mailings (radio buttons, YES/NO). Obviously there needs to be the corresponding form processing (with security) to commit the data to the database.

I've looked in profile.php and although I think it should be simple (I've written loads of form processing scripts) I must admit that understanding profile.php is a bit beyond me!

If anyone could help me create this addition, or point me in the right direction I'd be very grateful.

--Alan