DO Dude has great advice, let me add my two cents worth. I too, am a sort of comeback kid. I was out of school for 5 yrs before I went back and finished my BS. I, like Old Man Dave, did not do well during my first attempt at college. I think that after 5 yrs, you are not really the same person and admissions committees are aware of this, so unless you were in jail I wouldn't worry about your past. If anything, it will work to your advantage.
What you must do now is get AWESOME grades, there is no room for srewing up. Get strong MCAT's, talk to everyone you can think of about your interest in medicine and volunteer in a place where you can really get some meaningful experience. I personally think that mentoring youth, teaching people to read, working on a hot-line, anything like that is better than volunteering in a hospital where you just get to watch patients and get in everyone's way. Wherever you go make an impression on people, so when you ask them for a letter, they have something of value to say! Good luck!