So, this page shortly describes how this page works. As you may have noticed, the URL doesn't change that much at all, when viewing the different links. That is because this is in essence only one page. This page reads everything it displays from a database file and shows this within a predefined layout. This layout is stored in a different file that is linked into this one to specify the layout and structure of the page.
The picture hopefully shows what I mean...
As you can see, the page also interacts with the database. Comments left in the guestbook are stored in the database and retrieved when viewing the comments.
As this is rather a simple design (and i mean really simple) I don't know what else to say. For a peek in the source code underlying this page, just walk by and i'll show you. :-)