True... are you really a fellow?
Anyway, just to answer your question. Check on the interview feedback section of SDN for samples of questions from schools you are interested in applying to.
The atmosphere of the interviews is extremely variable. Some schools favor a relaxed interview and have in place mechanisms to avoid interviewers carrying out what are called "stress interviews". Other schools do not, and so an interviewee would be at greater risk of finding him/herself face to face with a jackass. After school trends, there is also the random component of the person who will interview you. Their style is bound to be a matter of personal preference. Confrontational types will like to ask hard questions and put the interviewees in really awkward situations to see how they react, because they might deem this to be an important characteristic to know in order to assess an applicant. Other more relaxed interviewers can feel like they get a better idea of the character and motivations of an interviewee by conducting a relatively stress-free interview and asking questions nicely.
Basically, it will depend largely on the specific schools, and then on who happens to interview you there (which can be hard to find out before hand).
PS. Yes, you should prepare for interviews. Reading the usual questions and having good answers to them is a basic you should have. After that, shortly before your interviews, you should do mocks and even try to film yourself so you can see what you look like. These drills are a really good way to learn to manage anxiety/nerves. Lastly, although you would be at an advantage having thought about responses to habitual questions, you don't want to sound rehearsed. An obviously canned response detracts from perceived sincerity, so strive for a balance between over and under-preparation. Good luck!
