If one of your co-workers loves to chat at all the wrong times, there are several ways of dealing with the problem tactfully. Experts say that you should be diplomatic and show respect and compassion for the other person. Many chatterboxes are procrastinators who use banter to avoid the tasks at hand, and can be sent away if, for instance, you stare at your computer screen for long periods of time.
See "The Workplace: How to turn away the office chatterbox", Matt Villano, International Herald Tribune, January 2, 2006