Flyrail,
I don't know anything about New School's program (other than what I've read on this thread), but I had an interview at Juilliard last year--I was a nervous wreck (I had applied on a whim!) and if I had it to do over again, I would be more quietly confident and relaxed (easier said than done, to be sure!). I think I may have come across as a bit too starry-eyed and overly eager, if not plainly bowled over by the recognition, which I think can easily be received as gumshoe and "not quite ready". When you get a callback in acting, they say that they just want to see if you can do the same thing over again. I think with playwriting interviews, they just want to see that you are who they thought you were when they read your application. Clearly, they think you are amazing or you would not have gotten the interview! So you don't have to be a salesman (or woman), just be yourself. Just remember they already like you. That should give you a lot of confidence! Good luck! :-)