If you have the problem with the game crashing at startup
"Falloutnv stopped working..."
I tried atleast ten different solutions that claimed to fix the problem.

But this one worked for me:
right click Fallout: New Vegas in steam -> Select properties -> Select local files -> Click VERIFY INTEGRITY OF GAME CACHE...

For me three files failed to verify and had to be re-accuired.
After about 2 hours of googling i stumbled across a page that got me to try this solution to the problem.
Since im no hardcoe Steam fan i had no clue that was possible.

Link: http://segmentnext.com/2010/10/19/fallout-new-vegas-errors-crashes-freezes-fixes/
I have tryed alot of the other fixes at that page and have not yet removed them, so it can be some kind of combo fix?