I would first check to see if PHP is installed and functioning. I do this by creating a page with only one line in it with the phpinfo() function.
This is one quick way to make sure PHP is installed and functioning and also a good way to learn more about your system. The whole line is simply...
<? phpinfo(); ?>
It sounds like you might not have the server configured though to recognize your file extensions (".php3 or .php4"). Are you running apache, or IIs, Xitami??