Adding a forum to your site?

Hi guys,

Im looking to add the most basic of basic message boards/guest books to my site. however i am useless when it comes to such things.

Where do i begin to add such basic guest book to my site?

http://www.zeekay.com/diamonds/diamonds.php -click on guestbook link

That is as simple as i want, maybe even more basic! Just name and comment, summit it, and it appears on the webpage.

Regards