The principles behind formatting a HD in an iBook is exactly the same as formatting a HD in any computer.
The computer has to be on and capable of accepting commands, however basic.
This usually means that the computer has to be booted into some sort of Operating System. On a Windows machine it is possible to boot into DOS, contained on a floppy, and tell the computer to format the drive. iBooks don't have floppy drives, as is becoming common on other computers. You could boot from an external drive, Firewire in the case of the iBook.
If you had an Ubuntu OS disk, maybe you could boot into that OS and format the drive.
Which ever way you slice it, which ever way you ask the question and however many times you ask it, the computer has to be booted into an OS for anything to happen.
Sorry
P