Do not try using custom boot images if you are running Jaguar 10.2.3 build 6H28 that comes with new Macs. I just finished rescuing a new 12" Aluminum Powerbook after manually applying a custom Boot Image extracted from another BootX file that worked fine on a Pismo in 10.2.3 Build 6G30. The modified BootX file rendered the AlBook non-bootable as the System Restore DVD did absolutely nothing to boot the Mac, even though the writing on the disk clearly states: "To start up from Mac OS X on this DVD, hold down the C key as the computer starts up." All I could get was an OpenFirmware prompt and none of the boot arguments that I knew at least would work to boot the CD.
I had to mount it in target mode on the Pismo to restore the file from a backup. After that it started fine. But for those who only have 1 Mac handy this can be disastrous. Hopefully Apple will release a fix to address the problem with booting these things from the system restore disk using just the C key on bootup. But for now: You've been warned!
[Editor's note: The boot image is the picture that displays when first starting the Mac -- there's a process to do this described in this article on ryandesign.com's website. Regarding this specific problem, it may be possible that the booting troubles with the restore disk were also caused by the problematic boot image -- it's hard to believe Apple would send a batch of machines out that couldn't boot from their restore disks ... I think the general warning here is that when you're modifying low-level things such as the boot image, you're never quite sure what may happen (especially if Apple has revved the system software version!).]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030213063923703