ok here's how its done...

You must have the FULL REGISTERED VERSION in order to use these codes.

First the cheats only work while your in the main game its self (your blowing
up missiles.)  Also, if you enter a cheat code you cannot get a highscore or
save your game.

So with no further adieu..

FIRST:

Press and hold ALT and type 4 2 0 on the numeric key pad.

Release the ALT key.

Now the action should have frozen.  Now type one of these keys:

S - SUPER shield, if yer gonna die do this one.

M - You now have a million dollars.

L - then hold ALT and type a number in the same fashion the 420 was entered
    the number you type will be your new level.  From 0 to 255.

E - End current level, make INCOMING change to 0.

there they are.. i hope i didn't forget any :)