Unlock All Stages - Put this code in at the menu screen.

Code Effect - Up, Left, Up, Left, Down, Right,Start Unlock All Stages

Unlockable Stewie Weapons

Collect different parts during the game then at the prompt, combine them.

Heat Seeking Warheads Collect 700 Parts
Hyper Plasma Ball (1) Collect 300 Parts
Hyper Plasma Ball (2) Collect 400 Parts

Plasma Artillery (1) Collect 200 Parts
Plasma Artillery (2) Collect 300 Parts
Plasma Ball (1) Collect 100 Parts
Plasma Ball (2) Collect 200 Parts

Rocket Launcher (1) Collect 500 Parts
Rocket Launcher (2) Collect 700 Parts

Shock Wave (1) Collect 400 Parts
Shock Wave (2) Collect 500 Parts
Spread Shot (2) Collect 100 Parts