The upcoming book was revealed in Tor's catalog for late 2009, which says the novel will be released in both hardcover and paperback editions. BioShock creator Ken Levine is listed as the author, although as Gamasutra notes, whether he actually wrote the book or simply provided the concepts upon which it's based isn't clear.
Tor Books is a well-known sci-fi and fantasy imprint that's published a wide range of authors including Orson Scott Card, R.A. Salvatore, Spider Robinson and Andre Norton. Tor has also published a series of novels based on the Halo games as well as the first book based on BioWare's upcoming Dragon Age RPG and is coming out with EVE: The Burning Life, based on the MMOG EVE Online, later this year.
The BioShock novel is scheduled for release in "fall 2009," which should put it somewhere in the neighborhood of the recently announced BioShock 2 launch on November 3 and make a nice double feature for fans.