Spirit-X

Easy way to beat walkers:
An easy way to beat walkers is to have a machinegun and flamethrower

A big Boom!!!!:
On the second level (when you get out of the helicopter for the second time). You will find a man in the building. heal him and tell him to follow you.after you get him away from the place he was you will see two canisters shoot them two times. after they explode use your fire extinguisher to put out the fire. In this room you will find ammo and a flame canister with one reload.

Simple Strategy 1:
Always keep your team members well stocked with arms and ammo, even if they are infected. It is easier to kill an infected member and take all his stuff then it is to backtrack trying to find more ammo.
Don't waste your medkits that determine DNA. If a team member is infected it will manifest itself in due time. Infact it seems to be scripted. I did a test on a member and it showed nothing. Then 5 minutes later he was a nightmare.

1st boss strategy:
Under the warehouse through a door is your first real boss. As soon as the cut scene has ended keep yourself to the left of the room keeping your back against the door. There is a tentacle that pops out of the wall on the right. Shot gun the hell out of the boss then use the flame-thrower on it until it collapses on the floor.
You will have to shoot the little spider things as your killing the boss because there is a hatching bubble just the other side of the boxes your standing next to on the left of the room.