The task you have is not very difficult for a web developer with even modest programming skills. Pulling in the content of an external text file is trivial using Server Side Includes, PHP, or even JavaScript/AJAX, but given that you also want to allow non-technical staff to edit this text file, I'd suggest that you set up a blog and take advantage of the reliability and security of the pre-built code. Check the control panel for your website's hosting account and see if they offer the capability of installing Wordpress or other blog software for you automatically. If not, installing one yourself is pretty simple, too.
