The best way to control anxiety is to focus on your physical actions. Believe it or not, controlling your body will help you quiet your mind.
1) Smile. Remembering to smile at the beginning of the interview will help tremendously.
2) Posture. If you are standing, your feet should be at roughly shoulder width. Do NOT rock or pace -- focus on maintaining a strong base. If seated, keep both feet on the floor. Although you want to maintain good posture (back straight, etc.), I have found that focusing on keeping your shoulders loose helps to keep you from getting too tense or anxious.
3) Gestures. If standing, keep your hands above your waist -- keep them out of your pockets, and don't place them behind your back or in front of your junk. Use gestures to emphasize your answers, but keep the motions reasonable since you don't want to be flailing around. Find a balance which is comfortable for you. If sitting, don't forget to gesture, though you may be restricted to using smaller motions.
4) Breath. Just before going into the interview, focusing on keeping your breathing slow and regular.
One other tip which may or may not help: To this day, whenever I have to do some kind of public speaking or performance, I always have a jolt of stage fright when I first begin -- I can't quite overcome my introverted tendencies. I have found that it's helpful to have an opening line or approach ready to go so that you don't have that awkward moment where you're thinking, "OMG they're all staring at me." If you're the funny or convivial type, a joke or small talk can work. For an interview, it could be as simple as mentally rehearsing the first few things that you do: walk in, smile at the interviewers, sit down, and say "Thanks for inviting me here for this interview." By scripting it out, you don't have to THINK...and once you establish a positive rapport with the group, you can relax and focus on the interview questions with confidence.
Good luck...