I'll give you my opinion on the interview. It is really laid back like everyone says. They try and keep you fairly comfortable here. Trying to get into medical school is stressful enough. What DMU wants to hear about you is this: who are YOU. Like dancinjenn said, be yourself.
With this said, I'll give you a few other things to think about.
The questions that I recieved were not terrible hard. The hard thing can sometimes be the fact that there is so much more to you as a person than what is revieled through answering the questions (this can be true of any interview). I handled this problem by making a list of personal attributes and accomplishments that I thought were important enough to be touched on no matter what question they ask. The hardest thing to do can be thinking on your feet and smoothly working these things into your answers...
Q: How do you feel that osteopathic medicine differs from allopathic medicine?
A: Well I don't know much about that, but I was president of my university's student government for 3 years.
This may not be a good answer. I think you get the idea. Like everyone says about DMU: just relax; you'll do fine. And you will. Just be sure to prepare.
things to think about...
personal attributes
personal weaknesses
why you would be a good fit for DMU
why DMU is a good fit for you
if your application here was turned in late, why?
what you have to offer to your classmates if you are accepted
why be a doctor (duh)
I'm sure you can think of a few more things to add to this list.
Good luck, have fun, be yourself.