If you press the escape key while ingame you will see the Unlock Content button. Press that and enter any of the following codes to unlock an item set.

Password - Effect

373624 - "Armament of Gaul" set
437626 - "Armament of Germania" set
925678 - "Garb of the Great Merchant" set
274267 - "Shinobi Shozoku" set
96958644 - Achilles' Spear
13333786 - Anendjib's Spear
63466346 - Ares' Wrath
53253253 - Armor of the Immortal Guard
12472353 - Fury of the Three Amazons
15662674 - Herod's Reach
85376494 - Horsemaster's Pike
14441522 - Monk's Spade
25356154 - Penetrating Spear of Ko k'Bi
53262633 - Raptor