using external drive to boot osx

Hi,

i have an ibook G4 with a broken hard drive and also an external hard drive. Could somebody explain to me how i can use the ibook with the external hard drive in place of the broken internal one?
I've tried connecting the external, inserting the osx disk and turning on the ibook while holding down the option key but the external drive doesn't show up. Does it have to be empty?

Thank you
Chris

You have to boot from the OSX disc by holding down the "C" key while starting the machine. Then you have to install OSX on the external drive and set it as the boot drive. You can access the Startup Disc option from the menu-bar while you are running the machine from the OSX disc (it's under TOOLS).

Since you have an iBook, which is PPC based, you can only install and boot OSX from an external Firewire drive, not a UBB drive.

Thanks. I've sorted it out now.