For the last few days I have been pissed about not being able to boot an iBook from a USB CD-Drive. Apparently this is only possible by using a firewire external drive. The bigger issue is that God forbid anywhere local have a firewire IDE enclosure... hell, I had a hard enough time finding a firewire cable......
.... Then I learned about something that I will gladly trade the ability to boot from a USB drive. This little gem is called "Target Disk Mode". The uses of this are really endless. Basically any drive in a macintosh computer can be used as an external firewire drive. Yes, you can do backups of your hard drive this way..... AND it allows you to use the DVD drive of another macintosh as a firewire drive.... which means if you have an ibook with a dead optical drive, you can use the drive from another mac by starting that mac in this mode.
1. Make sure that the target computer is turned off. If you are using a PowerBook or iBook as the target computer, you should also plug in its AC power adapter.
2. Use a FireWire cable (6-pin to 6-pin) to connect the target computer to a host computer. The host computer does not need to be turned off.
3. Start up the target computer and immediately press and hold down the T key until the FireWire icon appears. The hard disk of the target computer should become available to the host computer and will likely appear on desktop. (If the target computer is running Mac OS X 10.4 Tiger, you can also open System Preferences, choose Startup Disk, and click Target Disk Mode. Then restart the computer and it will start up in Target Disk Mode.)
4. When you are finished copying files, drag the target computer's hard disk icon to the Trash or select Put Away from the File menu (Mac OS 9) or Eject from the File menu (Mac OS X).
5. Press the target computer's power button to turn it off.
6. Unplug the FireWire cable. Reference Link