You can boot from your LaCie, sometimes it can be tricky on older machines running PPC.
First
-reset the Open Firmware
-Start the computer holding down "command" , "option" , "o" & "f"
-when the text shows up type "reset-nvram"
press enter
-then type "reset-all"
press enter
The computer will restart, hold down "option" and make sure the LaCie is plugged in to the iBook. You should now see your LaCie as a startup disk. select it and press enter to boot from the drive.
..done & done..