The trackpad is built into the upper case: http://www.ifixit.com/PowerBook-Parts/G4-Aluminum-15-Inch-1-5-1-67-GHz-Upper-Case/IF154-058?utm_source=ifixit_guide&utm_medium=guide_intro&utm_content=required_items&utm_term=powerbook_g4_aluminum_15%22_1.5-1.67_ghz