I took the MCAT this last August having had only one year of biology for non-science majors and one semester of general chem. I won't know the results until mid Oct., but I think I got at least a 30. Verbal reasoning is the section that I didn't feel comfortable with, which is the section irrelevant to this discussion.
I am taking the pre-requisites now, and I think that I would do better come April, but that might have more to do with the additional repetition than anything else. You can get a good score if you teach yourself, but it would take you at least as long to do it properly as if you had taken the courses.
In my case, I got mono in the first few weeks of the fall semester that I was taking physics, chem 2, and organic, and had to drop out. The community college where I was taking the classes (I already have my BA) didn't offer physics 1 in the spring, nor organic 1 until the following fall, so I decided to get a jump on those classes by studying on my own. Eventually I just decided to take the MCAT first without the classes, hoping that an adcom might at least be a little impressed that I could teach myself. I was self-taught in highschool too, so I am used to it.
However, if I had the choice now, I would probably take the classes before the MCAT. I have the feeling I would have gotten one or two more cheap points on the two science sections if I had. Should you decide to do it on your own, I would suggest that you buy a one semester organic book rather than a two-term book. The two-terms go into more detail than you need. Also, take many practice exams well prior to the exam, and perhaps take a Kaplan course if you can afford it. I didn't take a review course, but most people who have feel it helped.
Good luck, whatever you might do.
