This solution only applies to the old HUE webcams which required software drivers. If you have a new HUE camera, it's most likely that the camera is already in use in another application and iChat can't access the video stream.
iChat was designed to accept input from Firewire and UVC webcams. As the HUE is a driver-based USB camera, iChat required some additional third party software called iUSBCam to be installed on systems running Mac OS X 10.5 or earlier. Details can be found at the iUSBCam website.
Once you have installed the iUSBCam software please make sure that WebCam Monitor is completely closed (Quit from the WebCam Monitor menu or press Command-Q on the keyboard) before starting up iChat. In iChat select iUSBCam from the Video menu. Go to Change Video Source… and pick the camera from the dropdown menu.
For further iUSBCam questions please contact the creators at the link above.