the google ebooks page shows it works with the sony software, which as far as i know means epub. and the kindle doesn't support epub (yet, "they" say).
i would suggest you try your hand at converting but i'm not sure whether the google ebooks have DRM on them.
you can try the gutenberg project for free public domain books that are in a format accepted by kindle.
http://www.gutenberg.org/wiki/Main_Page