Above all Googlebase requires EAN and condition.
I need to find time to package the new version for you pips, holidays start in a week so lets hope ...
If you want to do it yourself you need to create a new database schema, then use hooks to tie this to the forms api, which is what i have done .
Then you get extra fields like condition, ean, etc etc these are then added to the feed .
Simple really if you know how.
Drupal 7 is easier to program , but then again you need knowledge of the system.
