I have an old 640x480 Intel USB webcam that I wanted to try with my 1st generation Mac mini (G4 variety). The camera is auto-magically recognized by Windows XP and works fine there. So, I was surprised how awful the image from it looked when I tried the Open Source...

maccam: USB Webcam Support for Mac OS X

But, your mileage may vary. So, if you have a webcam on the list of supported devices for this project and have a camera-less Mac, check out macmcam and see if it helps you out.