To take you back one step from where Bill took you, if you go to the bottom of the main page of the forum and look in the section called Forum Stats, you will see a statement "View the most recent posts on the forum". Click on that statement (link). That will give you ten pages of the most recent posts. There are ten posts per page, or a total of 100 posts. That's the total. There are no older ones.
This is a problem that I am faced with as a Moderator because I have to look at every post. If I want to reply to any post, I have to do it when I first look at it. Otherwise, I have to hunt it down later. Since we frequently have well over a 100 new posts a day, I can't always rely on the method discussed above to find a particular post.