I had a regional interview in Salt Lake for BU. It was the most laid back interview out of all of them. My interview was basically a chance for me to ask whatever questions I had and to tell them stuff about me. The interviewer left it pretty open ended for me to ask or say what I wanted. With that said, the interview lasted about an hour.
Research the school on the Internet and ask questions. Be prepared to talk about yourself as well and why you would want to live in Boston or go to BU.
Don't stress out at all (I know easy to say, but hard to do).