The above posts have pretty much covered everything about the interview process. The importance of reviewing your essays and résumé cannot be emphasized enough. Almost 90% of the conversation in the interview will revolve around this and how the road you've taken thus far ties in with your plans for the future.
One last thing, during the last few minutes of the interview, the interviewers like to talk about generic stuff which can range from anything such as the places you'd want to visit to the recent books that you've read. This might be the easiest part of the interview, but they're still looking for coherent answers - just don't be caught off guard!
If anyone has any more questions, or wants more specifics - fire away!