atcrofts idea is probably best, but you could have a look at using a wiki if the data is less static. Wiki's are usually open for anyone to use, but most of them have authentication options. You would need to alter the templates to make sure it doesnt look like a wiki to outsiders.
I'm using twiki at the moment, which has both authentication and easy to edit templates, however I'm thinking of moving to tikiwiki for various offtopic reasons.