How many USB webcams are you using? I'm not very familiar with Macs, so I'm sure one of the SKJM guys will jump in....but I do know that there is an issue with the USB bus power output being too low to power more than 1 or 2 cameras. If you have multiple cameras, try removing one and then see if you can see the C170. For the most part, virtually any USB camera should work with iCam...