Eidos just announced in a press release that an agreement with Microsoft was establish and XBOX players will receive two new downloadable chapters for Tomb Raider: Underworld, containing up to six hours of new gameplay.

The new chapters and a demo are going to be available on XBOX Live Marketplace. The demo will be release in October and the first chapter will fallow this Christmas.

Now, if you like, some “PR talk” from the press release:

“We are constantly looking at ways to extend our franchises, whilst developing a deeper relationship with our players. The retail release of any videogame is just the start of the player experience, from there it all depends where you want to take the player in terms of ideas and innovation,” said Sean Vesce. “With these additional chapters and the online reach of Xbox LIVE, we are able to deliver exclusive content to millions of gamers worldwide.”

“We’re thrilled that Xbox owners will be able to extend their Lara Croft adventures with exclusive ‘Tomb Raider: Underworld’ episodes,” said George Peckham, General Manager of Global Third Party Publishing for Microsoft’s Interactive Entertainment Business. “We look forward to continue working closely with our great publishing partners to deliver the most robust gaming experiences, only on Xbox 360.”