#653
BioShock is using the Unreal engine which has been massively modified by Irrational.
Originally BioShock was being built on an Irrational-modified version of the Unreal 2 Engine known as Vengeance. Since then it has been ported to Unreal 3.0 and has once again been heavily modified.
The game will feature some DirectX10 content for Vista users.