The two new maps are available over Xbox Live and once downloaded will be selectable from the game menu. The maps titled Surface and Communications were included in the recent release of Doom 3: Resurrection of Evil, a standalone expansion. Surface is an outdoor industrial yard, which provides plenty of sniping opportunities thanks to lots of scaffolding and narrow catwalks. Communications is set in a Martian warehouse and is full of dark corridors in which to blast away your opposition.
Remember that the Xbox Live service will be offline for 24 hours on October 24th so you better get gaming now.