There is a lot of programatic headache that can be accompanied by attempting to tackle the Google Checkout API. With the overhead of any online monetary transactions and three different layers of integration means a lot of documentation to cover. The gCartEncoder is a PHP library that allows you to alleviate some of the headaches and get an implementation of a phase one integration in place.
The gCartEncoder allows you to quickly and easily set up a phase one integration with Google Checkout. It allows you to skip all of the programming headaches of creating a google Checkout program to interface with their API and allow your site’s audience the ability to purchase items from your site.
Google Checkout API Instruction
Download gCartEncoder