Here's a good introductory article on acupuncture and a quick read. The author covers the basics of how acupuncture works and what a session is like. Some of my clients might disagree with the claim that 'acupuncture needles cause no painful sensations.' However, I think they'd agree that the short term discomfort is well worth the long-term gain.
http://pr-gb.com/index.php?option=com_content&task=view&id=6448&Itemid=9