If you remember the tank that comes rolling in at the end of the demo, you can run to the corner of the street before you kill everyone and as you kill the last person(or of of the least few), you can see the tank spawn.
Quickly shoot the the red caps of the gas tanks on the rear end of the tank before the cutscene is initiated and then the demo shouldn't end.
After killing everyone, I keep hearing another soldier which seems to be coming from this building with this turret peeking out of this window.
Also, I went to the body of the target's that you're supposed to kill at the end of the demo and he had this weapon i never seen from any other soldier. It's the Luger P08
Specs: GTX260; Intel Core 2 Quad Q9550 @2.8ghz; 4GB of RAM
HAY! I SAWL THIS POST ON EXBOX 360 BORAEDSZ!
^ probably lies ^