Photo Booth will see any Internal Camera as the default camera if nothing is plugged in before Photo Both is started.
There is no camera selection in Photo Booth
To Change cameras you have to Quit it and restart it with the required camera Plugged in.
This is the same in Tiger or Leopard.
Obviously you may not have an Internal camera on your G4 but the same would apply to a USB camera.
If Both are plugged in both iChat and Photo Booth will default to the Firewire camera as first choice.
In System Preferences > Displays is it set to Millions ?
3:05 PM Saturday; January 10, 2009
Good. The firmware is Up-to-date.
IS there any chance you have installed Perian ?
It is an Add-on/Plug-in for Quicktime to play or access other Video Codecs like DivX
If so do you know what version you are on ?
Some people are reporting issues with Chat's picture in 10.5.6 and Perian 1.1.3
8:24 PM Monday; January 12, 2009
No, I do not have Perian.
I have iChat 3.19 v446,
Photo Booth 1.2,
iSight Product Revision Level: 1.0.3
OS X 10.4.11 Tiger on a G4 MP500 tower, software up to date
Machine Name: Power Mac G4
Machine Model: PowerMac3,3
CPU Type: PowerPC G4 (2.9)
Number Of CPUs: 2
CPU Speed: 500 MHz
L2 Cache (per CPU):1 MB
Memory: 1.5 GB
Bus Speed: 100 MHz
Boot ROM Version: 4.2.8f1
Do you have another Mac User Account set up on your Mac ?
If so doe Photo Booth work there ?
Set up a test Mac User Account if you don't have one.
If Photo Booth works in the test account then return to the main account and go you your Home folder (Little House Icon)/Library/Preferences and delete the com.apple.photobooth.plist and try again.
8:11 PM Wednesday; January 14, 2009
In that case go to you Home Folder > Library > Preferences and delete the com.apple.PhotoBooth.plist and try Photo Booth again
If that deoes not work use this FAQ http://discussions.apple.com/thread.jspa?threadID=1486891&tstart=0
It is about Reinstalling iChat but Use the Hard Way and the PAcifist option to Install Photo Booth from the Install DIsk.
Also note the last paragraph and install the Combo Installer for the OS level you are at to Update Photo Booth.
10:17 PM Wednesday; January 28, 2009