You type

 NUMBERONEDACRESTREET

 at the main menu it brings you to a menu and you can get many
 cheats from there including 5 new secret levels...

 Hold down [Shift] and type:

 WIREWEWAITING       - Turns 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 in the moon
 HAVEALL             - You got it all
 SUPERDAISY          - One shot kills 'em all
 SUPERSHOOT          - Same as SUPERDAISY
 INVUNERABILITY      - That's just what it seems
 INFINITELIVES       - And so is this one
 INFINITEWEAPONS     - Infinite weapons
 MASTEROFTHEUNIVERSE - At least it changes textures on & off

 CHEATKEYS           -  Activates debug mode with thge following keys

  [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

 The starting parameters:

 -framerate"    Show frame rate
 -screenmode    Choose resolution of the screen
 -nolensflare   No lens flare effects
 -nofog         No fog
 -nosky         No heaven
 -nomipmap      No mip mapping
 -no3dsound     2D sound
 -noshadows     No shadows
 -nonetwork     No network support