Actually, thats not the cause at all. I think its the frameset you're using. All pages have the same URL if you click through the menu to your other pages. The URL stays the same. hmmm not sure what to tell you at this point.
I think the problem might be the frameset itself. It's src attribute is always set to "http://stmatthias.dnsalias.com" which retrieves the homepage. Regardless of whichever link you click, when the page loads it will come to the frameset part and retrieve the page pointed to by the src attribute.
So, i think if you really want to keep your frameset in your html, then in each of your .php pages, change the frameset src attribute to the respective php file.
eg. In about.php change the the frameset src to "about.php", etc
Try that and inform us.