Apple has posted a firmware update for the 550MHz and 667MHz PowerBooks (running Mac OS 9.1 or later) on the Support pages of its Web site. The firmware on these portables is now at version 4.2.9.
The 1.1MB firmware update improves the FireWire target disk mode when running Mac OS X, and startup on systems with 1GB . It also allows Netbooting over Gigabit Ethernet, according to Apple.
If you are using Mac OS X you must boot from a local Mac OS 9.1 writeable partition (not a CD, or network disk) prior to following the update instructions.