Congratulations on your accomplishments, Bunny. And congrats on the interview invitation. Are you applying for New Pathway or HST? Either way, interviews here tend to be very laid back. Last year I got asked about my research in some detail in the HST interviews and just a bit in the New Pathway interviews. However, since you have published in those great journals, I'm sure they'll ask you. But then you should have no problem talking about that. The interviews would be pretty much like those at other schools. Just relax, show some passion in whatever you are doing or want to do with your life, and enjoy the experience.
Stay with a student host if you could. No hassle taking the T to the school on the day of the interview. Our student dormitory is conveniently across the street from the school.
The medical area is a pretty boring social place. There's nothing but hospitals, research labs, medical institutes. If you have some free time, catch the M2 shuttle to Harvard Square, which is about 30 minutes away by bus. Harvard Square is a charming, vibrant place, especially on a not-so-cold weekend night when street musicians show off their skills and young people swamp the sidewalks. Visit the Harvard Coop if you want to see what a tourist trap is like. But visit Wordsworth for the best bookstore in the area. (There are about 5-6 bookstores in Harvard Square.)
If you're at the Square, try Penang for some extremely delicious Malaysian food or Spice for good Thai dishes. The best place at the Longwood medical area is probably Brown Sugar.
Walk around Harvard Yard if you have some time. That place is pretty amazing when you think of all the people that have walked across it for hundreds of years.
Bring the warmest jacket you have. I was just outside just a few minutes ago, and it was 5 degrees F!!!
Congrats again. I hope that you'll enjoy your short time here and that you'll get into the school of your choice.