I recommend a free
Discussion App from Server.com who are very nice people with a high degree of commercial integrity.
Their free boards carry ads, but leased ones (like the one I use on my own site) don't. You'll also find that a server.com board has plenty of flexibilty and can be customised to look just how you want it.
Plus, they do a lot of other great free stuff too. Tell them Rod H sent you, ok?