http://xbox360.ign.com/articles/758/758236p1.htmlA Microsoft representative confirmed to IGN that every copy of Crackdown includes an invite to the Halo 3 beta. If you want in on the beta (and didn't earn an invite by other means), purchase a copy of Crackdown on February 20 and you'll be set. You can even purchase a copy on February 21 or even March 15 and still be in the clear. Oh, and you'll get a copy of Crackdown to boot. Sweet!
http://gamersreports.com/news/3656/The british mag "GamesMasters" had a preview in their latest issue that disclosed that the deathmatch mode (featuring 16 players simultaneously) for Crackdown will only be available through the marketplace. No word if its free or will cost you points though...