I discovered this book after taking the test the first time and wanting to improve my score.  I had taken the in-class Kaplan review course (because my company paid for it), but I found that the questions from the "Official Guide for GMAT Review" and the sample tests from GMAC (the makers of the test) were far more similar to the questions I saw on the actual test.  Since GMAC makes the test, they're the only ones with the license to use old test questions in their preparation materials.  At the time when I took the test in 2001, GMAC mailed a CD-rom with two sample tests when you registered...