Start the game with the parameters "-redrum -stendek", so your command
line is "aqua.exe -redrum -stendek"
In the game itself (when your actually driving) use the following keys 
for the described cheats: 

Code     Result
------------------------
F7     - God Mode Toggle On/Off 
F8     - Invisible Toggle On/Off 
F10    - Mission Complete AUTO 
F11    - Mission Complete MANUAL 
F12    - Mission Failed