I bought Dead Money via. Steam, and it began downloading. I then clicked on Fallout: New Vegas, and it said it would be ready in about 15 minutes. After the 15 minutes, I startet the game, clicked the DeadMoney.esm (in data files), and started the game, but it simply opens Fallout: New Vegas. I've tried restarting Steam several times now, and I've even tried verifying the integrity of the game cache.. It then says "1 files failed to validate, and will be reacquired", but nothing happens.
In the steamapps/common/fallout new vegas/data/ folder, DeadMoney - Sound.bsa, DeadMoney - Main.bsa, DEADMONEY.NAM & DeadMoney.esm is.

When you say it opens New Vegas. Do you mean it loads New Vegas?

Yes exactly. I've now found, that if I keep verifying the cache, it keeps downloading small files (800 bytes or so), so it looks like I just have to verify it a million times to get it working.. I'll let you know.

So the game loads ok?

You can load and play no problems? Dead Money -like all DLC- is accessed through the game itself. You'll get a message when playing as normal if its activated.

*Note* You need a save game from before the 'Point of No Return' to play the DLC.

Not too used to DLC, so I'm kind of new to this.

The Fallout: New Vegas works like a charm. I've now created a new game and saved it, so I have a save game from before the point of no return. How do I play the DLC?

Just wait. You'll get a quest pointing you to where you need to go for it

So I just have to play the game as normal, and suddenly a quest will pop up?

Pretty much yes,

If it's anything like the Fallout 3 DLC, you'll get a radio signal on your pipboy, listening to that will give you a new quest.

Jep, got it.. Works Thanks everyone.