web page

i am building a web page for some friends of mine. they own their own small buisness and are wanting a web page for it. ive built most of it and its pretty basic. well here comes the question, they told me yesterday that they wanted their own discussion forum on there. like i said, i can build basic pages but dont know the first thing about a forum. any one that can help would be greatly appreciated.

is yahoo worth having host a website. if not any ideas