PS2 games cannot be played on a PS3 40 GB game system. Although certain PS3 models are compatible with PS2 software, the 40 GB game system is not one of them.
The 20GB, 60GB and 80GB PS3 game system models are software-compatible with PS2 games. All other PS3 models do not allow PS2 games to be played on their system due to the discontinuation of including the Emotion Engine and full PS2 circuitry required. Although the first three PS models allow for PS2 games to be played, Sony discontinued including PS2 compatibility in future models due to increased cost impacts.