2) Open a socket to the HTTP server and write out the HTTP headers and POST info. You can read the HTTP RFCs to find out the protocol; just search Google. Or search google for a non-RFC page about the HTTP protocol.
3) Use Unix Inter-process communication (IPC). I'm not sure if this is available for PHP, which is why you probably won't use it. But if you need to pass a ton of info, then use this.