If you are missing any of the prerequirements for med school, then definitely take them before the MCAT. If your physics isn't solid, retake it. You'll have to know formulas/concepts without any help from the test. I took biochem while I was studying for the MCAT, and I think it helped me a lot. They sneak biochem onto the test every time. You might also consider genetics or physiology.
If you're good at self-pacing, then studying yourself will be fine, but if you need structure, I would suggest a prep course. I took a prep course and was disappointed (Princeton Review). The course materials are great, but the instruction was horrible.
Many Texas schools will look favorably on you being an older applicant. Galveston and San Antonio come to mind for MD, and if you consider DO, TCOM will be interested as well. Southwestern may not be as friendly to older students. I had friends who applied at the same time who were 40 and 44, and Galveston accepted them both. I have friends in their 30's at San Antonio. I turn 30 this year and I'm going to TCOM.
Try to apply ASAP...take the April 2001 MCAT and you'll be admitted for the entering class of 2002. Let me know if you have any questions about the process. Good luck with everything!
------------------
We are the music makers, and we are the dreamers of the dreams.
--Willy Wonka