Apple has issued an updater for iBook G4s; "Graphics Update 1.0."
According to Apple's documentation, this update is recommended for the 12-inch 1GHz, and 14-inch 1.2GHz iBook G4. It updates the graphics driver to fix a compatibility issue that may exist with applications that use OpenGL. When this update package is downloaded and installed it will replace the old ATIDriver.bundle with a new one.
This update is not for all iBook G4s - it will apply itself only to 12" 1GHz or 14" 1.2GHz models.
For more information as well as a download, visit the Graphics Update product page.