Rockstar Games Brings Full Line-up to Steam - Jan 4th 2008

All your favorites from Rockstar Games are now on Steam! To celebrate, you'll save 10% on every title, from the complete Grand Theft Auto and Max Payne series to Manhunt, Midnight Club II, and more. Specially-priced collections and bundles are on sale, too, including The Rockstar Collection, which packs every Rockstar game for just $53.95 (regular price: $59.95). Hurry--the sale ends January 11.

See the full line-up of games and collections here.
well as far as i know Rockstar does not have a cafe licensing system, so it is possible that they will go through steam for it.
If they do, it wont be for awhile more than likely.