Start the game with abuse -edit and press [Shift][Z]. All you have
to be aware of is that the cursor has to be in the window during
this action. Now start the game with [Tab]...
To get direct to a certain level start the game with
abuse -f levels\levelxx.spe, where xx can be a number from 00 (first
level) to 21 (last level).
A nice thning also is the firing without ammo! If you do not have
enough ammo for a certain weapon, but you have enough for another
gun, you could use it nevertheless. Press the right mouse button
while you fire with the left one. If you run out of ammo for the
afterburner, you could use it and the ammo for the grenates will
decrease for one. This does not work with the laser unfortunately.