Umm... sure. I think what would do you best is using PHPNuke, Drupal, Geeklog, Xoops, Mambo. Something like that. They're all Content Management Systems (CMS). Basically, you as an admin give people permission to post where you want. It's the same idea as permissioning a forum.
Take a look at the open source CMS scripts out there to see if any suit your needs. Then, if you find something close, download it, and look at the code. See if you can understand what is going on. Any questions, ask.
~Brett