Quick form fix..

I have a form that when filled out in wordpress posts to a PHP BB forum. Currently, if someone enters the wrong captcha code, it loses all of the data in the form and they have to fill it out. I would like one of two things to happen, either: a. The form checks the captcha via ajax, and kicks back an error if it's invalid on the form without taking them away and keeps the page intact. or b. If the captcha is entered incorrectly and the user is taken away from the page, the data is stored in a session and they can retrieve it by going back or clicking a link. Nice and quick job for someone.