If you're starting out and have no money to spend, get phpbb. Both have great tutorials on installing. I still haven't found a great mod_rewrite for phpbb. All of the ones I've found still have bugs like the pagination won't work and things like that. The best thing to do if you're going to get phpbb is to download the archiver at phpbbhacks.com and pm me for instructions on how to modify it so it becomes simply a dynamic sitemap. Then you do the mod rewrite so it makes topic23.html but still has session id's, it's the only way to eliminate the duplicate content, keep the pagination and be spiderable. Unless someone else has some good articles on the mod_rewrite?