The DVD was not as bad as i thought..as it says on your letter it's about a dentist and a patient. You'll realise what you have to say when you watch it.
They mainly ask you questions about your personal statement and a couple about the dvd. If you look on here for sample questions and just work on those you should be fine.
The interviewers are really nice and they help you if you get stuck
ask me if you want anymore help