Hi Nicholas,
OpenACS CMS is a powerful system with an awful user interface. I would not use it in your case. Instead, take a look at edit-this-page. It's a simple "content management system" made especially for needs like yours. Of course, whoever updates the content has to have some basic html knowledge.
For announcements etc. you could use news or press packages.
You will need to do some custom hacking to build a working system with these building blocks but for the needs you mentioned you probably don't have to do anything from scratch.
