From the The Vault, the Fallout wiki:
Honest Hearts is an upcoming add-on for Fallout: New Vegas, developed by Obsidian Entertainment and published by Bethesda Softworks.Coming out simultaneously on Xbox 360, PC, and if it's working, PS3 next Tuesday, May 17th.
Honest Hearts takes the player on an expedition to the unspoiled wilderness of Utah’s Zion National Park. Things go horribly wrong when your caravan is ambushed by a tribal raiding band. As you try to find a way back to the Mojave, you become embroiled in a war between tribes and a conflict between a New Canaan missionary and the mysterious Burned Man. The decisions you make will determine the fate of Zion.