I went to the XBLM and saw a listing about MW2 and It read like this:

The best-selling Xbox 360 game of all-time just got bigger, with more epic multiplayer content, first on Xbox LIVE! The Stimulus Package delivers 5 additional action-packed multiplayer maps featuring a variety of locations: "Bailout," a multi-level apartment complex; "Storm," an open industrial park littered with heavy machinery; "Salvage," a snowy junkyard fortified by stacked debris and crushed cars. Two legendary fan-favorites from Call of Duty 4: Modern Warfare return, including "Crash," a war-torn urban environment; and "Overgrown," which features a massive dry creek bed. There are no refunds for this item. For more information, see www.xbox.com/live/accounts.

Visit this link (if it's still up) for the XBLM page. Since Robert Bowling will be on Major Nelson's show this sunday, he will verify this information.

Update: Here is the link in Major Nelson's show where Robert Bowling talks about the stimulus package for Modern Warfare 2.