To be honest, interviews are pretty relaxed for research positions. You should know the basics about the research, but they know it is over your head; its okay.
Most professors hire undergraduates KNOWING that they're incompetent and have to be trained. They're ALL incompetent when they start.
The important things you need to get across in the interview:
1) You're proactive and independent. In a lab we need people that will actively find research papers to read in order to solve their own research problems.
2) You like working on difficult problems, and with your hands. If he asks if you like cooking, you do. If he asks if you like puzzels, you do. Common sense stuff.
To sum it up, my PI once told me, "given a difficult puzzle and 3 job applicants, I would not hire the guy that solved it in 5 minutes, I'd think he's seen the puzzle before and is cheating. I wouldn't hire the guy that gives up after 10 minutes either, because he's easily discouraged."
You want to be the guy that will diligently work on the puzzle for two hours, solve it, and go looking for another puzzle to solve. That is the essense of research.