GTchick,
Bring some other shoes for the tour -- and they typically won't last an hour either.
I winged my interview for the most part, although I always tend to keep myself current with events in the profession as well as world and national news events (when worse comes to worse, these are great conversation pieces).
Spend an hour looking at the school's webpage and reading any literature they might have sent you. Research the city you are going to also. In the interview, be proactive and ask some questions that you have though of beforehand (and don't feel that you have to rely on the typical questions. Interviewers probably are sick of hearing about board scores, etc.).
Ask how the school is involved in the community, what feedback the community has given to the school, what life experiences are unique to the dental school, and how these experiences are woven into the curriculum, etc. etc.
Good luck!