i used the CD based practice questions very breifly. i found them to be sorta lame. not great questions coupled with outright crappy explanations. stick with kaplan or usmleworld.com
i used usmleworld, and it seemed to prepare me exceedingly well for the question type and content. usmleworld was actually more nit-picky than the real test, but the explanations were great. i went through all the questions once, and then started reviewing them, and i felt decent taking the real step 2. don't know my scores yet, though.