iMovie HD 6 and iMovie '08 include features which require Quartz Extreme. Quartz Extreme is a technology included with Mac OS X that utilizes advanced visual capabilities offered by modern graphics cards.
If you install an additional graphics card that is not compatible with Quartz Extreme in your computer (so that you can attach another display), the features listed above may not function correctly in iMovie. This is true even if your original built-in graphics card is Quartz-Extreme compatible. The additional card must be compatible with Quartz Extreme, even if you will not be displaying your iMovie project windows on the display connected to it.
iMovie requires that all graphics cards in the computer be compatible with Quartz Extreme. Note that Quartz Extreme requires millions of colors.
See Mac OS X 10.4: Requirements for Quartz Extreme and Core Image graphics for information on how to tell if you have Quartz Extreme functionality.
Note: With iMovie 6.0.2 and later, when you open iMovie with non-Quartz Extreme compatible graphics hardware, you'll get an alert message that says:
"Your computer contains a graphics card which may not support iMovie. iMovie requires a 'Quartz Extreme Compatible' graphics card. Certain iMovie features such as Themes, Ken Burns Photos, and Video FX may not work properly with your graphics card."