For the full version

Press [Enter] during the game and type in:

In the german version:

SELFDEFENCEAGAINSTFRESHFRUIT     Units invulnerable
SPOTTHEBRAINCELL                 1000 XP for selected units
MONEYSONG                        1000 prestige points
MRHILTER                         100 x air support etc
MOTORHEAD                        One hit kills
BICYCLEREPAIRMAN                 Unlimited load for repair truck
DIRTYHUNGARIANPHRASEBOOK         Win mission
THEFUNNIESTJOKEINTHEWORLD        Kill own unit

In the english version:

SheepInTheTrees                  God mode
FreeWestMemphis3                 God mode
TheFunniestJokeInTheWorld        Kill own unit
SpotTheBraincell                 1000 XP for selected units
MoneySong                        1000 prestige points
TheSpanishInquisition            One hit kills
Inferno                          One hit kills
BicycleRepairMan                 Unlimited load for repair truck
SelfDefenceAgainstFreshFruit     Units invulnerable
MrHilter                         100 x air support etc
DirtyHungarianPhrasebook         Win mission

For the demo version:

SHIELD                           Units invulnerable
SMARTEN                          1000 XP for selected units
MO MONEY                         1000 prestige points
TOP GUN                          100 x air support etc
KILL BILL                        One hit kills
ACME                             Unlimited load for repair truck
ZEUS                             Reveal all units
JUMP                             Win mission