Really good tute :-)
Can I make a couple of suggestions?
1 - Put your include files in a special include directory. I use things like /incs/global/, /incs/ads/ etc etc, especially if you use a .html file extension.
Otherwise you run the risk of losing / forgetting what they are! (You could also use .htmlincs or something as a file extension and get Apache to read it as a FileHandler).
2 - Ideally, place include files (esp php ones, like DBConnect) outside of the webroot, so in your html, you have to reference the include as
Code:
include("/outside/webroot/path/to/file/include.php");
This means people can't access them by typing
http://www.blah.com/include.php