Don't use interview books. They turn you into a cookie cutter premed with such rehearsed responses that banality would be a severe understatement.
If you want to prepare for interviews, here's how I did it, and it may not work for you, depending on what you already know about certain issues and what type of person you are. NEVER SCRIPT ANYTHING OR USED SCRIPTED MATERIALS. Always develop informed opinions that are your own. I prepared alot, only because it relaxed me, others like to fly in raw and play it all by ear, it depends on you.
I first look over stuff about myself: PS, secondary essays, my EC's and what I learned from them, my major, publications, thesis, etc etc. Then I look over stuff that isn't about me per se: healthcare issues, bioethics, current events, etc. Books like Healthcare Meltdown, Understanding Health Policy, and also the UWash Bioethics module are great. I also read some other books for leisure, like HoG, On Call, etc etc, there's a book list that I maintained floating on a thread somewhere in PreAllo, search for it.