Enter the following passwords at the title screen, password option:

Password - Effect

B7FG4 - Level 2
XTV5P - Level 3
TV5DP - Level 4
FXGNL - Level 5
HGRSV - Level 6
K7DGR - Level 7
FTXCG - Level 8
G5J4H - Level 9
CRDTS - View Credits