Earlier this month Microsoft announced something called the Xbox Live Arcade Block Party promotion. Here are additional promotion details and the release schedule.
Here are the details from Major Nelson:
March 3rd: Toy Soldiers -1200 points
March 10: Scrap Metal - 1200 points
March 17: Perfect Dark - 800 points
March 24: Game Room - Free to download.
Individual games will cost 240 to 400 points
Plus: When you purchase all three Block Party titles and download the free Game Room app you'll receive 400 Microsoft Points back to your account. And if you're an Xbox Live Gold Members you'll also get an extra month of Gold absolutely free.
And from Noon ET Friday, March 26, - Noon ET Monday, March 29 Block Party is making it easy for you to play together with an Xbox Live Multiplayer Unlock weekend. For this weekend only, we're unlocking the online multiplayer features of all Block Party titles for Silver Members to play for free (games sold separately).