If you type NUMBERONEDACRESTREET at the main menu, it brings you to a cheats menu and you can get many cheats from there including 5 new secret levels...
Hold down SHIFT and type:
WIREWEWAITING = Turn off the textures.
WHATSTHEPOINT = Turns graphics to the dots.
SOLIDASAROCK = Invulnerability.
FLATBROKE = No shading.
GOURAUD = Gouraud shading on.
OLDMACDONALD = Protect farm from jumping COWS!!!.
FLYMETOTHEMOON = Racing on the moon.
HAVEALL = You got it all.
SUPERDAISY = One shot kills 'em all.
INVULNERABILITY = You're THICK if you don't know what this does!
INFINITELIVES = Same with this one...
INFINITEWEAPONS = Infinite weapons. (This is getting tedious...)
MASTEROFTHEUNIVERSE = At least it turns textures on and off...
Cheatkeys:
F2 = Easy Shoot.
F3 = Invulnerability.
F4 = Infinite Lives.
F5 = Infinite Weapons.
F6 = Smart Bomb.
F7 = Quit.
F8 = Stores current situation.
F9 = Reloads stored situation.
F10 = Frame wait on/off.
F11 = Restart