Firstly, enthusiasm is the main thing. It really comes across well at interview, and if you couldn't care less, the interviewers pick that up straight away.
In terms of further reading, I read a couple of books that I'd put on my personal statement, and after re-reading before my interview, I got asked nothing about them at all. However, that's not to say that you won't - I got asked nothing general at all in my interview, whilst I know other people at other colleges who did. Be prepared, but further reading isn't that necessary.
What is required, on top of the enthusiasm, is a solid understanding of what you've studied so far. Both my interviews started out with basic questions on what I have done for A-level (and the bits of Further I'd covered), but by the end of both I was working with stuff I had never seen before and needed prompting from my interviewers. What they want is to see how well you think and will be able to cope with the course, and not necessarily what you already know.
I hope you understand that - because on re-reading I don't...