The little mic you refer to is a lavalier mic, or simply called a lav mic. They can either be wired or wireless. The Azden system I recommended is wireless. The person being interviewed has box (the transmitter) with the lav mic attached appropriately to his/her shirt. Then the second box (the receiver) is mounted on top of your camera and its output is plugged into the microphone jack on the camera.
This video describes the system and shows how to use it with the Canon (http://www.youtube.com/watch?v=uYlhDGrw_eA)
Heidi
