If you, or someone within the company, has pretty good programming knowledge, such a web site is relatively simple to make with a programming language like PHP.
If you want the easy way out though, there are lots of free and good alternatives out there that could do the job for you. If you actually want a full fledged web site though, I would not recommend something like SMF that staktas recommended, because that's merely a forum engine. If you want to set up a web site that allows for all the things you mentioned, you should look into a CMS (content management system) such as Drupal, or even something like WordPress which can be used in a similar fashion (and is extremely easy to use, maintain and customize). Though WordPress is primarily a blogging engine, it can also work extremely well for the type of web site you're looking for.
But if you want the most flexibility, you want to create your own web site. Perhaps there's someone within your company capable of doing it, and otherwise there's plenty of web development companies and/or freelancers out there that should be willing to do it for you.
So yeah, tons of options out there