Jeff may disagree with me on this, but here's my take on interviews.

Know your stuff, but if you can't answer the question, be honest about it. Tell the interviewer that you don't know. I've told prospective employeers before that "I don't know the syntax, I usually check BOL before I do it" or "I haven't played with that functionality before" or things like that, depending on the question.

In my book, there's nothing wrong with those kinds of answers. And if the interviewee seems to know the other stuff, but is weak in an area or two, I'm willing to let them learn on the job, so long as they're not trying to BS their way through the interview.