Really, truly, Purza, I suggest you sign up for an "Overcoming Exam/Interview Anxiety" course. Even rehearsing interviews with a friend can help a lot. The interview-er wants you to be comfortable, too. Employers genuinely want to find the best candidate for the job. They can't do that if you are wringing your hands, stumbling over your answers, and sweating bullets.
I do really well on interviews. I take care of the small things beforehand so that they don't distract me. I've read the annual report and done my research on the company. I am dressed well, every hair in place. I arrive twenty minutes too early and spend the first ten in the washroom (before introducing myself to the receptionist) to fix hair, shoes, stow extra bags, etc. etc. Hey, this is the great white north, we are always carrying weather wear. I make sure I have only a small clutch-size carrier with me (less stuff to fuss with). Ten minutes before the interview, I introduce myself to the receptionist (direct eye contact, broad smile, firm handshake), take the seat and anything else offered (you don't have to DRINK the coffee). When I am introduced to the interview panel, I give direct eye contact, warm smile, firm handshake. Hands in lap, don't fiddle, smile. I'm on. At the end, warm handshakes all around, and DON'T FORGET TO THANK THE RECEPTIONIST. Done. Don't worry. If you've flubbed up, it's too late to fix anyways.
I, too, hate those questions designed to get you to talk about your weak spots. With any of these kinds of questions, I give a mild real-life example (let's not freak them out!), identify my weakness (shows that I am aware of my own shortcomings), and ALSO LIST THE STRATEGIES I have used to manage my weakness (I show that I constantly strive to improve).
The best answer I got for "deal with a difficult co-worker" was from a girl who gave a real-life example from someone I know. I agree, dealing with that particular woman requires the patience of a saint. She has managed to frustrate every one of her co-workers with her high-handed or unreasonable requests. The office staff have a rather unflattering nick-name for her. This young girl gave a most insightful answer, "I realize she has no family, no outside interests. Work is her life. I try and understand from her point of view, and accommodate where I can. If her request is unreasonable, I call her on it, and if I need to, I involve her supervisor."