Be very familiar with your research. My experience wasn't necessarily that anyone went after me, but it was helpful to review details of everything that I did (or rather, said I did in the application
). Sometime, faculty will not get the general gist of your research because they're reading it in brief and will pick out some mundane detail you thought was relatively unimportant, so its critical to be able to defend/describe in further detail everything you said you did.
IMHO, the MD interviews took much less prep than the PhD ones. Come with a prepared answer for the strengths/weakness question, the ethical dilemma question, and the why medicine question. Although honestly, I didn't really get too many of those. You'll be surprised how much of your interview is just chatting.
Oh and before I forget, its absolutely critical that you prepare a decent amount of questions about the program that you can ask faculty. If you only have one or two that they answer over the course of the interview, and they ask "so, do you have any questions?" at the end and you say no, thats bad. Everyone asks you for questions at the end, IMHO the interview should go on another 5-10 minutes after that. Good generic ones include asking about the quality of clinical training, how they and their colleagues combine their clinic and research (if they do), if they've had any MD-PhD's in their labs and how they've done, what sorts of fields their graduates go into, if they think an MD-PhD is particularly relevant in their field, etc.