Update: Before you download this demo, take a look at the 2k Forums. I installed it and wish I had not.

 The demo for BioShock, the genetically-enhanced shooter from 2K Games, is now available on Steam.

BioShock will be available via Steam and at retail on August 21 in the U.S. and August 24 in Europe. For more information or to pre-purchase BioShock, click here.
Source

The demo for BioShock, the genetically-enhanced shooter from 2K Games, is now available on Steam.

BioShock will be available via Steam and at retail on August 21 in the U.S. and August 24 in Europe. For more information or to pre-purchase BioShock, click here.
Source