I would suggest, as others have, using a CMS. I personally use Joomla on over 17 domains, and have yet to find an issue when using the user-controls. I can setup as many members as I want, with differing permissions for each user-category I create - some are super-users, who can create/edit/destroy any content they so wish, others can only add/edit article content, and some can only view registered content while the "public" or guests can view any non-registered content.
check it out:
http://www.joomla.org
Totally free and open source

Super easy to setup, modify and use!