For a good prep book check out "Checklist for Success" by Cheryl Cage (the same person that does the interview prep in Denver). It's a great read, very fast, tells you what you need to know and only $20. I used it and aviation interviews.com questions to prep for mine. I did not do any official prep but I know there are some that feel the need to, and others that might benefit from it.

Either way that book is a great launching pad to get you started if you can't do the face to face prep right now. It really gets you thinking.

Another thing I did was read off some questions to people I was working with. I can tell you the way something comes out in your head might sound completely different to others. I find women tend to take things different than men as well. Also look up some psychology type things online, ie how does an interviewer tell if someone is lying? Not that you would, but it's important to understand that you need to tell the truth (or base it on a true story) and it's almost impossible to make something up and get away with it. There are tons of resources online and on Youtube (search for "Behavior interview"). All this can be done before you walk into the prep office if you still decide to do it, it will allow you to get more out of the experience.