Ooooh, good luck! Those interviews can be scary, but for me the "right" ones ended up feeling very comfortable once I was there and talking to people. (It seems so logical when one isn't under the immediate pressure that if you have to present yourself as something you're not in order to "make it" someplace, you're not going to be happy there, and if you're not happy, you're going to have a harder time succeeding. On the other hand, if you click with your interviewers and start to bounce ideas around and stray from the initial topics, then that's a good sign that you're probably going to fluorish at that institution, IF they have a program that's got what you need.)

Best wishes! :-)