Personally I read textbooks, took some SAT tests at home on my own, and when I checked the sample tests of Jag, I saw that its ok.. if you already have some background in bio+chem (for Jag, and phys as well for other schools), only to refresh yourself and solve some problems should be enough. If you dont have backgorund, still you can do that on your own at home (I think you have time to prepare for the entrance tests). But of course to join a program or to have a personal tutor helps for discipline as well.
By the way, I benefited Student Doctor Network's MCAT forum to find answers for my questions. Also Chemical Forums - Index helps a lot.