Well, researching I found this:
WEBCAMS FOR OBSOLETE MACS? OSX 10.2 or OSX 10.3 PANTHER?
Think FireWire instead. Modern high-resolution UVC cams simply WILL NOT WORK on old 800mhz or less Macs, who's slow and incompatible USB 1.x speed ports are FOURTY times slower that USB 2.0. Those that claim to be USB 1.1 compatible in their Specification listings may have utterly abysmal frame-rates on USB 1.x or show NO image at all, even though Apple's System Profiler may recognize the camera exists on the USB 1.1 bus. Otherwise you're left dinking around with any of hundreds of old, discontinued webcams made for Windows and fiddling with Macam or IOXperts drivers hoping for a combination that will work.
You CAN still find decent, used Apple iSight cams at Amazon or find a deal on an iSight on eBay. Why Apple stopped manufacturing their very high-quality 1394 FireWire auto-focus web camera is beyond logic. 1394 is better than USB for video conferencing and chat in many technical aspects: External FireWire webcam compatibility with iMovie, less CPU overhead, higher frame-rates and avoids USB device contention slugging it out on a USB hub. USB cameras aren't the only options to provide Macintosh users with high quality choices to chat and videoconference using popular Mac OSX applications like FaceTime, iChat AV, Yahoo Messenger, Apple Messages, Skype, ISPQ VideoChat. Or, for capturing and uploading clips to YouTube or other video sites.