What helped me in interviews was my experience volunteering at a free health clinic. I was able to talk about healthcare disparities for minorities and the uninsured from a statistical point of view and from real life experience. I just read up on Obama's plan, healthcare systems in England and other Western European countries and compared them to our current healthcare system. I looked at our system from a supply and demand viewpoint and looked at the pros and cons. Also, I read books by Atul Gawande and Jerome Groopman. They talk a lot about ethics for physicians and mistakes doctors make and how to change them.
I have had 2 interviews at allopathic schools and 1 at LECOM-E. Only one of the allopathic interviews lasted longer than 20 minutes (it was 1 hour). In that interview, we were able to talk about insurance issues, problems with the pharmaceutical industry, and the lack of adequate amounts of physicians. The other interviews were only 20 minutes and I only had time to tell the interviewers about myself and maybe touch briefly on my view of the biggest issue in healthcare (large number of uninsured people). I wouldn't worry too much about having a large grasp of healthcare knowledge for interviews. Just make sure you know some basic issues in healthcare today.