If your webcam is dark or has color-balance problems, i Glasses can correct and help compensate for many image quality issues.There's several other Mac webcam effects and image apps worth checking out as well, notably Mactaris' Mac webcam app utility downloadable from the Apple App Store. If your processor is a G4 or greater, if it's speed is 867mhz or faster, that's the point where Apple built-in USB 2 speed ports. In Apple System Profiler Device Tree -- USB 2.0 devices listed need to show "Speed: 480Mb/sec".You may have to launch, relaunch Photoboth, un-plug, re-plug your external Mac web cam to get Photobooth to recognize it, but it's doable. But it's the video capture or chat programs you use often can't take advantage of it.
Apple intentionally does not allow external USB Mac webcams to be selected as a video source in i Move. Try a special hack from Mactaris that allows i Move to 'see' an external 3rd-party web camera.
Otherwise you'll simply need to record your video with some other Quick Time compatible video capture app - then bring it into i Movie for editing.
Old USB 1.1 ports-devices will only show "Speed: 12Mb/sec" as thier maximum bandwidth. Modern USB 2.0 high-resolution UVC webcams utterly overwhelm USB 1.1 ports which are more than FOURTY TIMES SLOWER.
Some cams won't display anything - or if they do you'll find your Frame-Rate is so abysmally low you'll just end up in sluggish, slow-motion frustration.
Apple's built-in i Sight HD on the i Mac, Mac Book and Cinema Display line have horribly limited camera angles, so adding an external Mac webcam gives alot more flexibility.
Particularly for adult sex web conferencing you want and need moveable, adjustable cameras.
Most Quick Time compatible apps allow selecting and switching between multiple video sources on the fly; Nice and Civil to Down 'n' Dirty.
Fire Wire webcams can often be daisy-chained or be shared on a Fire Wire hub.
Selecting which cam to use is done within the programs Video Settings...
similar to switching audio input sources between a built-in, external, or a Bluetooth headset. Trying to run Photo Booth, Skype or i Chat and perhaps another video app simultaneously - One app will put your webcam 'in use.' If And When you initiate a video call - the other app(s) can't share that.
Sometimes just canceling one app's video call & switching works, sometimes you have to Quit competing video apps and relaunch.