Cheat mode:
To acess Cheat mode press the following sequence at the Main menu
X
X
Y
Y
Click Left Analog-stick
Click Left Analog-stick
Click Right Analog-stick
Click Right Analog-stick
L
L
R
R
If the combination has been entered correctly you will hear a confirmation sound and the Cheats option will be unlocked at the Options menu which will include Trooper Level, Enemy Al and Mission List selections.
Weak spots on tanks:
To have any chance of destroying heavyly armoured tanks you must attack them with an explosive at their rear which is lightly armoured. Smaller tanks can be destroyed by a rocket almost anywhere.
Destroy SCUDs:
The Sniper Rifle can blow up SCUDs by shooting the rocket in the launch position.

Mine fields:
Destroy tank mine fields on certain levels by throwing a grenade which will make them all explode.