The product release page has cover art and discussion of the Dark Sun Campaign Guide. I don't think such a thing exists. There's a Dark Sun Campaign Setting, and a Creature Catalog. I think the Campaign Guide morphed into (and was renamed to) the Creature Catalog.
I can't find a "Dark Sun Campaign Guide for sale anywhere or listed on the WOTC site.
I could, of course, be mistaken...but the Campaign Guide link on the product release page goes to the Creature Catalog page on Amazon