Glad to be able to help.
I just found this on Logitech's website for your Quickcam Vision ProMacintosh OS X:
USB drivers are already installed in Mac OS X. If you are experiancing problems with OSX's audio drivers, run your system update from the Apple Menu or use the "Disk Repair" utility found on your OSX Install Disk. For more information about how to perform these functions, please visit Apple.Com's Support Website
I wanted to bring this to your attention, because it does make me wonder about this aspect, that Logictech is not providing very much support in the way of Mac OS X interface with this Quickcam Vision Pro model in regards XXXXX XXXXX audio portion of this product.
What I would also like you to try per Logitech Support's recommendation is to run Disc Utility to repair permissions via your Mac OS X 10.4 Installation disc, because you are set up correctly as far as your webcam goes.
-RUNNING DISK UTILITY FROM STARTUP DISC
•Insert the Mac OS X Install disc that came with your Mac,
then restart the computer while holding the C key.
• Keep holding the C key until you see the White screen, Grey apple and eventually the Spinning gear.
•When you see the Spinning gear, then release the C key
• Allow your Macto continue the booting to the CD.
• You should see the language screen which will lead you into the Installer environment
• Once in the Installer environment, from the first window and from the Installer Menu bar, select Utilities.
•Now choose Disk Utility from the Utilities menu.
Important: Do not click Continue in the first screen of the
Installer. If you do, you must restart from the disc again to
access Disk Utility.
• Click the First Aid tab.
• Select the hard drive icon displaying your Macintosh HD
• Click Repair. Disk Utility checks and repairs the disk.
• Once completed, quit Disk Utility
• Click on Installer Menu and reboot to your Mac Desktop
So try this process and then check your Quickcam again.
Let me know if this helps. Thanks!