Which version of he iBook G4 do you own?
Go to the Apple Icon top left and to 'About this Mac'
Let us know the details.
Most have an Airport Card installed under the keyboard which can be easily removed.
The later 2005 (1.33Ghz 12" and 1.4Ghz 14" ) models have the airport cards built-in.
You could try resetting the PMU to see if that helps.