Adding tags to menus

Hi all,

I want to structure my WP menu in such a way that the parent items on menus are categories, and the links underneath are tags, which when clicked, display all the relevant posts.

This is what I want to accomplish: I have a number of contributors to a site who will be writing on topics that will be relevant to a number of different sections on the site. The way to organise these would be tags, but how does one go about integrating that taxonomy into a dynamic menu?

Thanks in advance.

James