(1) See the " WEBCAMS FOR OLD MAC? " section here: http://www.mac-compatible-web-cam.com/
(2) In addition to firewire webcams, before OS X 10.4, I used my firewire connected Sony (other brands can also work) mini-DV camcorders as webcams. They work just fine, and they offer the added benefit of producing better image quality than webcams of that time period. If you have a Firewire equipped mini-DV camcorder, connect it and give it a try. You may be able to gather some more info out of this old page that has been heavily edited for more modern solutions: http://www.ralphjohns.co.uk/EZJim/EZJimpage8.html
(3) If your Mac(s) do not have Firewire ports, present day USB solutions may be more difficult to find.
(4) In addition to the cautions in all the above documents, verify the minimum system requirements for every software application you plan to use to operate your cam. Failure to meet some of the minimum requirements other than camera type may prevent you from using your Mac(s) regardless of which camera you choose.
A clear example of such requirements is shown in iChat 3 for OS X 10.4: http://support.apple.com/kb/HT1771
Another example is the iChat AV 2.1 that is required for video chat with OS X 10.3.9 has lower requirements. I can no longer find document
http://support.apple.com/kb/TA27456 on the Apple website, but its information is available here: http://tinyurl.com/73u2xmx Your G4 Macs meet the processor requirements, but you will need to verify the other system element requirements if you plan to use iChatAV2.1.
I am going to expand on this by way of some history.
iChat 2 effectively got released with OS 10.3
It was the first AV version of iChat.
At the time Apple were making and selling the External iSight which used Firewire to connect.
Very soon an add-on appeared to be able to use the USB (1.1 versions) cameras that were about.
(it actually did two jobs. Allowed the External iSight to work with below spec Macs and also allowed USB cameras to be used)
This Add-on Utility needed the Ma to have a driver for the camera. This meant the camera had to have a Mac driver or be able to use one of two Third Party Drivers.
As EZ Jim has said other Firewire camera could and would work including DV convertors.
So up to this point we are talking aboout USB 1.1 cameras with Mac Drivers (or Third Party ones) and the iUSBCam utility or a firewire camera of some sort (Or something connected to a DV Convertor)
At OS 10.4.10 the OS had a USB Video Class Driver added.
This allowed USB 2 Cameras that were UVC (USB Video Class) compliant cameras to be used without any other driver.
At the time these were generally sold as "Vista Certified" or were marked as UVC compliant on the box.
You do have to have USB 2.0 ports for this to work. (Some Keyboard ports are Not on older Desktop Macs)
Currently it is very difficult to get USB1.1 Cameras to take advantage of the ports on older Macs.
It is also true that DV Convertors also have moved away from Firewire as USB 2.0 is just a bit faster.
CAMERA TYPES Driver (or Not) Additonal Info USB 1.1 Needs Driver for Mac (Possibly Third Party) Plus iUSBCam Utility Firewire No Driver needed Can be a DV Convertor - preferably Firewire USB 2.0 No Driver needed (part of OS) May restrict older USB 1.1 Macs
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously