How2 open Guestbook in center of site rather than whole page

Sorry to ask such a newbie question for somthing that seems like it should be simple. But........

How can I get my guestbook to open in the main area of my site while leaving my header, blocks, and footer intact. (Like the guestbook here opens up) My guestbook opens and covers the whole page. No more headers, blocks, footers, ect.

I know this must be basic PHP knowledge but I can't find the answer anywhere.
Thanks in advance.

The easiest way to do this would be with iFrames.
You could embed the PHP code but that could be somewhat troublesome if you dont know what are you doing

I use Iframes on all my sites with this guestbook and it works fine.
Drawback to this is that older browsers (ver 4 and below) will not "see" these frames

Let me know if you need more help.

There might be a better way, but I just added the code for index.php & addentry.php to the html code for the webpages that I wanted to display them on and saved them as .php files. I only used these two files because they're the only two anybody will see when they sign the guestbook.