GNU Distance Calculation - for the world in php

I have a way of getting the distances from one zip code to the next in the US, but I need to be able to do that for other countries as well. I've found a web site on the net that sells a database of all postal codes and their longitude and latitudes but they want a $1000 which I am not willing to pay, especially since I got all the US zips for free. Anyone know where I can get a database with all the postal codes and so forth or perhaps a couple different ones and hopefully the code in php to calculate the distances. I need to be able to at least do major countries in the world from one place in that country to the next. Thanks