I replaced my rear cover last night. I bought a new one on E-bay, and the Pro Toolkit and replacement clips from iFixit. Other than some cringing while removing the strongly-glued battery and soft foil antenna & cover from the rear cover, it was fairly easy. I wrote a story here:
[http://www.ifixit.com/Story/5201/iPad_rear_cover_replacement|Link]
It isn't a full guide, but it might help.