Install an original Airport 802.11b card internally.
Turn the G4 over.
Remove the eight T8 Torx screws from the lower case.
Using your thumbs, slide the lower case away from you.
Lift the lower case off.
Your laptop should look approximately like this.
Firmly grasp the plastic tab attached to the Airport card and pull up and to the left.
Disconnect the antenna cable from the left side of the Airport card.