iUSBCam allows you to use a USB webcam for video conferencing.
Editor: iUSBCam is an add-on for iChat which allows you to use a USB WebCam for video conferencing. It also enables Chat video conferencing on Macs which otherwise fall below Apples system requirements for conferencing.

For example, with iUSBCam, you can use a Logitech QuickCam for video chat, or an iSight with a 500 MHz iBook.

More Features:
Use most USB webcams with iChat.
Videoconference on a computer that iChat does not support.
Adjust camera settings like brightness and contrast.
Use a DV camera on a G3.
Adjust all iSight settings.
Videoconference using your screen as a video source.
Easily switch Between available video sources.
Try before you buy. Download the demo.

Change Your Video Source

iUSBCam adds Change Video Source... to the Video menu. This lets you quickly switch between available cameras.

Complete Video Settings Panel

iUSBCam adds a Show Video Settings menu item to the Video menu. You can use the video settings panel to adjust camera settings such as brightness, contrast, sharpness, and saturation. When using an iSight, many other settings will be available. Also, with some USB drivers, the More Settings... button will allow you to adjust camera-specific features such as face tracking
Broadcast Your Screen

iUSBCam will allow you to use your screen as a video source. Choose Change Video Source and select Screen View. The Screen View option is available even when no camera is connected. you can free download iUSBCam 2.2.4 now.