Well, I suppose you've looked through HotScripts and all by now. I hate to inform you that the concept of a real-time clock programmed in PHP is basically impossible.
JavaScript is a client-side scripting language which means, your browser parses the code at load time and executes the code.
PHP is a server-side script, which means a Web server parses the code and executes it prior to sending HTML to your browser. In order to create a real-time clock, you need to use a client-side technology. Some other client-side examples are Java applets, and flash animations.