I had php (the default install in Panther) up and running just fine in Panther. I recall editing a couple of lines in a cong file to get it up and running. While working on code I would keep my php files in my sites folder, and use my localhost to view them in Safari.
I upgraded to Tiger a little while ago, and just tried to access some php code to make a change or two to a script.
The php engine does not appear to be up and running. When I load the page in Safari, it just shows the script, like it is a text file.
I would assume the config file that I edited in Panther was replaced with a default one in Tiger that has php turned off... but I cannot remember which one it was.