Who do I contact to get the rights to show a movie for a charity event?

At my school, a teacher and I are trying to organize a movie night for charity. So far, we're in the initial stages of planning it, and we're trying to figure out who we would contact in order to get the rights to show the movie we've decided on (Grease, by the way). Anybody know who I need to get in contact with in order to do this?|||Contact swank.com. They have distribution rights on Grease.