Classified Ads scripts with session authentication

I have googled, and there are scores of them. We have our own database (MySQL) which we use to authenticate subscribers for out news site; does anyone know of a classified ads script that uses a session (or a cookie) to maintain authentication info? If so, we could provide our own front end and use the rest. I know this is a long shot - thanks for having a look. Regards - Miles Thompson PS What we want to do is enable subscribers to place ads for free, but have them available for anyone to look at. /mt