Hidden ammunition
When you first start the game, go in the elevator. When the doors open, enter the room to the left. You will find a crowbar. Hit the soft drink machine and get out of its way before it crushes you. After it falls, you will notice some gas spraying out. Jump over the machine and crouch down. Go over to the little hole in the wall at the back of the machine. Press E (Use)to shut off the little valve and the gas will stop spraying. Go in the hole, turn on your flashlight, and climb the ladder. Keep going and the floor will fall. You will now be in a secret room with shotgun and pistol ammunition.
Running from the monster alien
When you are right at the end of the demo, get to the right side of the platform and keep running against the edge. When the monster approaches to you, he will hit a computer and it causes the platform fall. Keep running to get past all the debris. You will be able to run around for a short time before the demo ends.
Undead scientist
Under the dome building where you go down a manhole to the sewer (because the entrance was blown up), is a man in the corner who is not dead. Shoot him twice when you are talking, and he should stand up and run. That is all he can do.
Extend demonstration...