100,000 money:)
While playing the game, PRESS START, then hold R1 + R2 + L1 + L2 and press X, Left, Right, Up, Left. You wills see a message at the bottom of the screen if you have entered the code correctly.
User Cheat by SlimShady

100 population:)
While playing the game, PRESS START, then hold R1 + R2 + L1 + L2 and press X, Right, Right, Left, Up. You wills see a message at the bottom of the screen if you have entered the code correctly.
 

Mission skip:)
While playing the game, PRESS START, then hold R1 + R2 + L1 + L2 and press X, Up, Up, Left, Right, Left. You may need to repeat this code until the confirmation message appears. After that, quit your game. When you get to the debriefing screen, press X to advance to the next mission.

Replay every mission:)
While playing the game, PRESS START, then hold R1 + R2 + L1 + L2 and press X, Up, Up, Left, Right, Left. . Now, quit your game, then go to the replay menu to have all missions.

All view:
While playing the game, PRESS START, then hold R1 + R2 + L1 + L2 and press X, Left(2), Right, Left. You may need to repeat this code until the confirmation message appears. This code will allow you to see all enemy units and buildings.

Mission 4: Releasing Hooper from prison:
Get one of your commandos into the prison. The prison will explode, and your commander will still be standing there. Take him to the northeast village and avoid the GHOST troops.

When you want to save Hooper from prison, take two Commandos, one Tank, one Mobile Artillery, and two Bazookas. Send the rest to the outpost by the right slope to get on top of the hill. Wait until they start blowing it up. Then, take the remaining men you held and go to the base. Blow up the prison with Commandos. There will be no men or machine gun bunkers. Then, send him to the flag at the northeast village. Do not worry -- there will be one or two men, but Hooper is strong and will make it without fighting.

How to Attack faster:
Build structures that make units (Barracks, V. Factories, etc.), then have each of them to make units. For example, if you made two Barracks and told one to make fifteen soldiers and the other to make fifteen soldiers, both barracks will make them. This works for both IPC and GHOST. This trick will allow you to make soldiers and attack a lot faster.