Serious Sam Cheats

Go to single-player and then go to the password screen. Now enter DUCKAROO. This takes you to the first Rome level.

Level - Easy - Normal - Hard:

Amon Thule - HEXMODE - OPEE - WOLF
Baths Of Diocletian - NEED - OWL - LIMO
Ceasar's Palace - WAFTY - MOOPAY - MOCKNEY
Forum Of Mars - GAMES - DUCKAROO - FOZZER
Gladiator Training School - COINAGE - FRYUP - MADEUP
Preatorian Fort - NORTHERN - FILLY - MIRROR
Pyramid Entrance Maze - BADDUN - BETTERER - CHIPPER
Slave Compound - BOBBINS - PILCH - FORREST
Slave Quarters - TOAST - BEVIL - BEAK
Temple of Herkat - Lower MNIP - KIPPAGE - TITHES
Tomb Of Ramses - MEGAMUNT - HORSE - EYE