The only way to get started is to start...
The first thing I'm going to do is go through the readme and installation files that come with the Google Checkout mod and rewrite and present in a much improved fashion.
The documentation here will then include (with screen shots):installation / editing of files
I also can say with confidence that one of the reasons this mod is such a problem is that we all tend to not read every detail of the files that come with the mods. We're all so used to throwing up the files, fixing the admin settings and running with it.
This mod, however, requires intense attention to the details that are in the original files as well as proper setup in one's Google Checkout account that isn't comprehensively documented for the Zen Cart community.
Anyone wanting to donate time (writing, research or screen shots) or money to this effort, please either use the PayPal button for donations or the contact form to email me.