Many iBook G4 laptops (and possibly other models) have a problem with the inbuilt AirPort card failing, and then causing regular kernel panics. This can be avoided in Leopard, and possibly Tiger, by replacing the kexts responsible for the AirPort

1. As soon as you turn the computer on quickly turn off AirPort in the menu bar.

2. Open TextEdit and save two blank files to the desktop. Name the First one  IO80211Family.kext.rtf and the second one AppleAirPort.kext.rtf. Then go to the Desktop and remove the ".rtf" extension, and approve the change to a .kext extension. These are the dummy files.

3. In Finder, go to System > Library > Extensions, copy and save to a USB stick, then delete the files AppleAirPort.kext and IO80211Family.kext and authorize the action. Then drag the two ‘dud’/blank kext files from the Desktop into the Extensions folder, and again authorize the action.

4. Reboot the Computer 

Keep copies of the original files in case you want to replace the airport card. The problem is likely to be the connection to the logic board so in many cases, so replacing the card probably won’t work.

An alternative, once you have either disabled the airport card with the software trick above or actually removed the old AirPort card, is to use a USB 802.11b/g Wifi adapter/dongle in one of the USB ports.