You should go back to your friend's house and play some more MW2. I would show you this EPIC MW2 movie like video on youtube but it has MAJOR spoilers in it and we wouldn't want that, would we?
You don't actually have to shoot any of the cilvians in that mission, only the SWAT team. Unless you run past them. I saw the ending of that mission before the game was released so I wasn't surprised at the ending.
And hello there bud. MEDIC! ERECTING A DISPENSER! THERE'S A SPY CREEPING ROUND HERE!
YOU GOT STEAM WORKING????