If you buy an Xbox 360 before Dec. 21, Microsoft will send you a free copy of Halo 3, the company announced today.

According to the official Xbox web site, gamers who buy a new console between now and the deadline, sign up for a new Xbox Live account and register their systems with Microsoft will receive a copy of Halo 3 in their mailboxes.

The game will arrive by Jan. 18, Microsoft said.

The deal isn't combinable with other Microsoft offers or rebates and is limited to one submission per person.

Hear that? That's the sound of a million holiday wish lists exploding.

Update: This morning, Xbox.com was advertising this initiative on its Halo 3 Deals & Promotions page. By this afternoon, however, the page was gone. This link to the promotion's registration page still works, though. We've contacted Microsoft for clarification on the deal, and we'll let you know more as soon as possible