Bioshock: Preview @ GamersInfo

Since the city was a utopia before the war broke out, there were no weapons. Every weapon that was created in the war and afterwards has been cobbled together out of regular household items. After breaking into a bar you are shot at by a sentry gun that is built into a chair. After setting off alarms you are attacked by a mobile sentry that is built out of an outboard motor. Even the weapon you are carrying is a hand made gun crafted out of various items scavenged from around the city. This theme of improvised weaponry continues throughout the entire game.