O.k. here's the scoop on the practice tests. AAMC V and AAMC VI are the most representative of the actual MCAT today. V is from 2000 and VI is from 2001. Get your hands them and when you do, DO NOT TAKE THEM until you have thoroughly prepared yourself for the MCAT. I'd recommend taking them perhaps a couple weeks before the MCAT, this way they'll be a decent indicator of how you'll actually do. Otherwise they are a waste. In addition take them under standard test conditions with the regular breaks. Oh, and do not skip the writing section when you do them.
AAMC III is reportedly quite easy compared to the real thing so I never really bothered with it. I know nothing about AAMC IV. AAMC I and II are essentially worthless since they date back to the early 90s like '90 or '91. If you get them, use them to practice your passage skills or to simply test some of your science knowledge.
One little warning about these tests. As I understand it, and someone correct me if I am wrong, they are each an amalgamation of passages found in the 15 or so different versions of the MCAT at each sitting. In other words AAMC VI was compiled from passages found in 30 different test versions, 15 from April 2001 and 15 from August 2001. They are not "real" MCAT exams so to speak but they can be a fair measure of how you will really do give or take 2 or 3 points. Even the scale they give you to convert your raw scores on these tests to a composite MCAT score is purely an estimation. On the real thing your score will be normalized along with the scores of each person that took your specific version of the test.
Hope this helps.
