The medical school where I work is in the process of setting up such a system with typo3. The people running the system from the top need to have good technical knowledge, but for the various departments, it's quite simple. As far as navigation and style - the school has a "default" style for any departments who don't want to set up their own, but there's a lot of flexibility for any who want to be different (although they might need some help from the IT people running the program).
I've seen statements from people who've tried to use typo3 as a CMS for a single website and complained that it's too complicated, but that's not really what it's made for. It's made for the kind of situation you're talking about.
We've implemented Mambo and Joomla for several schools. Either system works well. Might want to look at what functionality you require and see who has what out of the box. Drupal is also a popular choice.