If your Airport Extreme is a Broadcom bcm43xx, its a pretty quick fix.

Open the add software application, and install the bcm43xx_fwcutter pagackage. It could be called something slightly different.

Then, open a terminal.

First enter sux, and then your password when prompted. After that enter /sbin/install_bcm43xx_firmware. Resart your iBook and you're all set.