In your software update.
This software update provides improved performance and stability with iMovie 3.
For more information on iMovie, see http://www.apple.com/imovie
The requirements for iMovie 3.0.2 are:
QuickTime 6.1 or later
Macintosh computer with PowerPC G3 or G4 processor (700 MHz or greater G3 recommended)
256MB of physical RAM
Mac OS X v10.1.5 or later (Mac OS X v10.2.4 or later recommended)
1024 x 768 screen resolution or higher