According to Apple TIL #106236 (“Mac OS X 10.0: Included 9.1 CD Cannot Start Up Latest Computers“) you cannot boot a Macintosh released on or after January 2001 (PowerBook G4 Titanium, Power Mac G4 Digital Audio, Flower Power/Blue Dalmatian iMacs or CD-RW G4 Cubes) with the Mac OS 9.1 CD-ROM that comes bundled with the retail version of Mac OS X.
You will only be able to boot Macs released on or after January 2001 with the Software Install CD-ROM that came with your machine. Titanium users: make sure that you carry the gray Mac OS 9.1 CD-ROM in your PowerBook bag in the event that you have to re-install while on the road.
