The Google Earth Blog has been writing about the work of James Stafford. First he created a a size comparison of every moon (natural satellite of a planet) in the solar system larger in diameter than 100 km - all 34 of them - viewable in Google Earth. Download the 34 moons KML file here (4.5 Mb). See the original release at his Barnabu blog. You can see it here at Google Video.
Then, Mr. Stafford changed the Earth into the Sun (by adding an image overlay) and scaled down the Moons relative to the size of the Sun and added all the planets as 3D models. The result is a a true-to-scale comparison of the main bodies of the solar system. You can download it here: Google Earth Solar System (7 Mb).
Read about it at his page, (http://www.barnabu.co.uk/solar-system-in-google-earth/), and at the Google Earth Blog page (http://www.gearthblog.com/blog/archives/2007/07/the_solar_system_in.html).
You can watch it here, or go to YouTube.com