Assuming I am right about what your asking, a simple registration form will be very easy to do, especially if you can make the search form work
Simply setup a form, and post it to your php script.
Get the data ($HTTP_POST_VARS), do any validations on it you need, and use the INSERT command for mySQL (instead of the SELECT command you are using for your search form).
If I have assumed your problem is much simpler than it really is, I apologize, but from what you wrote, this should be a very simple project for you.
-Jared