Another option is to install it from another machine using Firewire target disk mode. Basically link the two machines with a firewire cable and boot the iBook (the "destination" machine) into target disk mode by holding the "T" key down during startup until the firewire icon starts dancing around the screen. The drive of the iBook will appear as a hard drive on the other machine. Start the Tiger installer disk on the other machine and select the iBook's hard drive as the install destination disk. It will install Tiger onto the iBook and then, bizarrely, restart with the new Tiger system on the iBook's drive over firewire. Switch off and disconnect the machines from each other and you should have a happy, Tiger-running iBook.

This is a good way to install from system-specific Mac OS installer disks and also for installing certain OS X versions on unsupported machines. And yes, this method does work with Leopard installers too!