Hi I have done it before. Good fun but hard work so be prepared! They will try there hardest to put you off doing the course on interview day - it is quite a clever way of sorting out those who really want to do it.
You get a tour, a welcome lecture and an interview as well as just a few written questions (don't worry about these it is just to check that you can read and write as you have to complete a large project during the course)
Enjoy and just be yourself, go with an open mind - you will either think it is or isn't for you.