Cool Kill

If you run up to an Iraqi with the knife in your hand and press R, sometimes, your soldier will go behind the Iraqi and stab him in the heart.

Multiple Weapons

Requires 3 or more people. Give the weapon that you would like everyone on your team to have to one person, then kill him. While he is lying on the ground, the other team members walk up to him, and hold down A when it says "Take From", and scroll to the weapon you want, but DO NOT press L. When everyone has the weapon highlighted, press L at the same time, and you will all have the weapon; although, you will all have the same ammo supply (when one person shoots the weapon, a bullet will be taken from everyone). This is a very good glitch when used with the "Unlimited Ammo" cheat. (At the main menu, press L(2), R(2), X(2), Y(2), B(2); this will unlock the cheat menu, available from the "Options" menu; besides having unlimited ammo, you can unlock unlimited saves, set your teams trooper level to whatever you want, set the enemy trooper level to 0, skip to a mission from a mission list, and, during gameplay, there is a "Next Level" option)

Cheats Menu

At the main menu screen, press L Trigger, L trigger, R trigger, R trigger, X, X, Y, Y, B, B. If done correctly, pause game during a mission, go to options, and a new cheats option will be available at the bottom. you can set it to save infinate times, have infinate ammo, trooper level, enemy level to 0, mission select, and skip to next mission.

The Land Of Glich!

On the ninth mission, after you get to the place where the 2 tanks and missles are, on the left theres three doors. Go to the second door, and the door is locked, but tell your men to stay back and with any one marine crouch down so your stomach is on the ground and move so that your facing the side of the door. Then start to roll into the door, if you did it correct your screen will turn white inside the room. After your inside just have fun, while nobody sees you. If you don't like it any more just simply walk out where there is land.

Shortcut Upstairs

On the ninth mission after you do "The land of glich" tip, switch players and move the second person to the same door as the first person did, then do the same code as the first person did to get inside that locked door. Switch back to the first person that was in "The land of glich" and the two players will be upstairs, but if your not, then with your first person tell the second person to come to you. Switch back again to the first and you'll be upstairs.

Ride In A BMP

After the mission you escape from the POW camp, Chemical Warfare or something, you can actually drive one of the BMPs. Once you get into the chemical plant, a cut scene will show an Iraqi getting out of the BMP. Keep going down the stairs then kill the Iraqi running at you. Now, go up the stairs in front of you and you'll see the BMP around the corner. Run up next to it and hop in and do some destruction with the 30MM machine gun.

Stealth

On the 4th level, after you drive up to the mines and get out, be Foley, and go up the little ledge. Command your men to stay back. Then, just take out all of the guys you can see. Foley has a silenced sniper rifle on this level so they won't notice you unless they see you. Try to make all of your shots head shots or upper torso shots. You'll know when you've killed every guy in that area because it will say "Objective Completed."