I am also someone who went to law school, and even practiced law for three years, and I am now applying to medical school. I think it can help you in some respects and hurt you in others. You have to demonstrate to adcomms that you are serious about medicine and that you have put a lot of time and effort into your decision. People told me my biggest problem will be explaining to adcomms why I gave up on medicine seven years ago. My situation may be different from yours in that I was pre-med in college, applied to medical school (20 med schools to be exact), failed to get in, and for reasons I've mentioned on other posts, I would up going to law school instead. Big mistake on my part!
Having a J.D. will set you apart from other applicants, and that can be good. I feel that I have a very interesting and attention grabbing personal statement because of my experiences (although most of these experiences relate to practicing law, i.e. working with the indigent etc., rather than law school itself). The most important thing is that you show them that you know what you're getting into and that you can explain why it took you so long to make this decision. You must have some clinical experience, or adcomms will question whether you are truly dedicated and have a real understanding of what you're getting into.
In summary, I've been told that it will work against me in some respects, and it will work for me in others. Med schools might be concerned you're a "flake" for taking so long, and moving from a completely unrelated field into medicine. So, you have to take steps to show them you are certain of what you are doing and truly dedicated to medicine.