In a recent article that goes into more detail about the PC requirements for their upcoming game Bioshock Infinite, Irrational Games' Technical Director Chris Kline stated that the game will not support Windows XP and that the PC version will require Window Vista, 7 or 8.
Mr. Kline didn't go into further detail as to explain why the game was not supported on Windows XP, but one could surmise that the game requires DirectX version, such as 10 or above, that is not available for the Windows XP Operating System.
He went on to add that the game will be compatible with Windows 8, however it will not be certified to do so. The game will use the standard Steam DRM, so a Steam account and an internet connection will be required when you install the game, but will work fine in offline mode when an internet connection is not available. Boxed versions of the game will come with a Steam key, so using the disc for installation or playing the game is not required.
Hit this link to check out the PC Requirements for Bioshock Infinite.