The cheats here are a bit more complicated than in other games. 
There is a two step procedure to active the cheat mode. (This cheat 
mode only works in the registered version. It does nothing in the 
shareware version.)

Type [C] [H] [E] [A] [T] at the Main Title Screen. All keys need 
to be pressed one at a time. When you get it, you'll see the message 
that says "Cheat Active" (it really isn't yet). 

During the game, hold down the [backspace] key, and then press 
the [H] & [S] keys at the same time. When you are successful, 
you'll see a message that says "Cheat Mode On" (it is now). You can 
hit these three keys again to turn the cheat mode off. 

Once activated, you can press these keys to activate various options. 
Please note that you must hold down the [tab] key first before
pressing the others, or it won't work. 

[tab] [O] - Fire Options
[tab] [R] - Rapid Fire 
[tab] [S] - Shield Options 

