Microsoft is hoping to muscle in for a hefty slice of the digital download market, which is currently dominated by Steam, by adding a Games on Demand service to Games for Windows Live.

On December 15, Games for Windows Live will include a portal for accessing and downloading your favorite live-enabled titles…courtesy of Games on Demand. Games on Demand for Windows lets you purchase and download titles from the Games for Windows live library right from your computer, and re-install your games whenever you want, wherever you want.

The launch lineup will include Resident Evil 5, Red Faction: Guerrilla, and Battlestations: Pacific, as well as new exclusive live-enabled versions of digital games such as World of Goo and Osmos, distributed by Microsoft Game Studios. All games can be purchased either by credit card or with Microsoft Points. Microsoft is also offering an updated live-enabled version of “Tinker,” formerly an exclusive Windows Vista Ultimate Extra, as a completely free download from the Games for Windows Live client.

To download the Games for Windows Live client visit www.gamesforwindows.com/live .