Type in the following on the faxmachine and press the white button (from the two biggest on the right the one on the back)
7287 - after you win the level, you can play a rat shoot level
24328 - Enables in-game cheats
Ctrl C - All deseases and machines of the level
Shift C - Increases money
Shift Ctrl C - All deseases and machines of the game
Ctrl M - End of the month
Ctrl Y - End of the year
Ctrl E - Activate an emergency
Ctrl S - A doctor with special capabilities
Shift I - Changes the desease of a patient
Shift 1 - Increases the number of patients
F11 - Lose current level (never worked for me)
F12 - Wins current level (see above)