Here's a quick (and hopefully easy) tutorial on how to properly setup Magento with Google Base aka "Google Shopping" or "Google Content" .
I know there is very limited help for Google Base/Shopping for Magento Community Edition 1.6 and 1.7 (and nothing official exists on any lower versions)...
The interested fact is, Magento is knowingly supplying a broken extension with 1.6 and 1.7--i.e. there is no way it will work unless you hack the core code; as we will below.
Hopefully, the community edition will get a working extension soon, just like the Magento Go version.
Anyhow... on to self help!