Eidos Interactive announced an agreement with Microsoft today that will make two brand new downloadable chapters, containing up to six hours of new gameplay and content, available exclusively to the Xbox 360 version of the next Lara Croft adventure, Tomb Raider: Underworld . Available for download via the Xbox Live Marketplace, these two exclusive chapters will be available this holiday season and early 2009.

The two new chapters are called Tomb Raider: Underworld – Beneath the Ashes and Tomb Raider: Underworld: Lara's Shadow , and both are meant to deliver two very diff erent single player experiences. Beneath the Ashes , scheduled to release this holiday season, takes place after the Underworld story and will feature an incredible new environment to explore, additional secrets to unlock and different enemies to fight. Lara's Shadow , currently scheduled for release some time in early 2009, is supposed to introduce players to “a new kind of playable character” and create a Tomb Raider experience. Clearly they haven't quite gotten as far with Lara's Shadow just yet.

The announcement that these chapters are coming exclusively to the Xbox 360 version of the game should give the sales of that version a bit of a boost. George Peckham, General Manager of Global Third Party Publishing for Microsoft's Interactive Entertainment Business said, “We’re thrilled that Xbox owners will be able to extend their Lara Croft adventures with exclusive Tomb Raider: Underworld episodes. We look forward to continue working closely with our great publishing partners to deliver the most robust gaming experiences, only on Xbox 360.”

Tomb Raider: Underworld E3 2008 Trailer

Tomb Raider: Underworld is currently scheduled to release on November 18 ^th for Xbox 360, Playstation 2, Playstation 3, Nintendo DS, Wii and PC and is not yet rated. A demo for Tomb Raider: Underworld will also be available for download via the Xbox Live Marketplace later this month.