http://www.amazon.com/USMLE-Step-Qbook-Kaplan/dp/1419551493/ref=si3_rdr_bb_product/103-6995784-7695800
I have the 2nd edition (copyright 2005) of Kaplan Qbook. I just did a side-by-side comparison between my Qbook and the 3rd edition Kaplan Qbook (using Amazon's "Search inside this book" hyperlink). You know what? The two editions are almost exactly the same--even down to the page numbers!
For examples, page 43 is Anatomy Test One and page 187 is Microbiology Test one. Both editions organized their questions by subjects. So, the only differences I see between the two editions are the front cover and the back cover.