Valve announces release details for The Sacrifice, saying the DLC is due for release on October 5 as separate dowloads for Left 4 Dead and Left 4 Dead 2. The PC editions will be free, while the Xbox 360 editions will be 560 MS points for each game. Here's word on the two different versions:

In The Sacrifice for Left 4 Dead 1 gamers receive the complete Sacrifice campaign with maps playable in Campaign, Versus, and Survival.

In The Sacrifice for Left 4 Dead 2 owners receive "The Sacrifice" campaign playable with the Left 4 Dead Survivors. In addition, those with Left 4 Dead 2 receive L4D's "No Mercy" campaign. Both campaigns are playable in Campaign, Versus, Survival, and Scavenge modes and both will feature the Left 4 Dead 2 Special Infected, items, and weapons. Yes, Zoey with a chainsaw!