Geoclassifieds Auto RIch HTML Newsletter engine

I have a script installed called geoclassified enterprise by http://www.geodesicsolutions.com. I have 96% of the site finished, but need help a php module that handles the existing internal newsletter fuctionality. What I need, is an option added to the registration form that allows users to select if they want or do not want to receive an email that is generated each day mailing a list or link of the newest items added to the classifieds over the last 24 hours. Currently I have a cronjob I am working on that kinda does what I want, but it is kind of a convoluted way to do things, plus I don't know of a way to make the registration form work with the cronjob, ie. how to make it send with a "yes" i want the email or "No" i don't want it. I have done quite a bit of modification to the software and it is pretty simple to modify. please let me know if you have any questions. Thanks BK