Sounds like a CMS (Content Management System) system..
http://www.opensourcecms.com
You can look at dozens of Content Management Systems at that site, view doemos of the various software as well as play in the admin interface.
Postnuke or MDPro are fairly easy to configure and get running, if you use godaddy for hosting they have a 1 click install of several popular CMS Systems such as postnuke, Joomla, Xoops, etc.. You can assign permissions by user, allow certain users the ability to add posts, or manage specific parts of the system.