At the beginning of Operation Little Saturn, in the Russian campaign (it's one of the tank levels), turn immediately to your left and find a single tree sitting on the slope of the embankment that doubles as the level's collision wall. Drive up the embankment directly to the right of the tree and right through the level's collision wall. From here turn to your left and locate a road that follows around the mountain away from the rest of the level. Continue down the road and in about 30 seconds to a minute to should see a large red apple in the distance. Continue driving into the apple to find one of the strangest thing I've ever found in a WWII game... Besides a 20 story giant red apple, at least.
All Levels
At the level select screen hold Up on controller two and on controller one press Start, Select, Select, Square.
Big Red Apple
In the Russian campaign, right at the beginning of the mission Operation Little Saturn, turn left and find a scraggly tree all by itself along the embankment. Go over/through the embankment just right of the tree, and then turn left and find a road that leads away from the rest of the board. After a while you will see a huge red apple in the distance. You can drive right through it to find something else that doesn't belong in a WWII game.
Cheat mode
Successfully complete the game under the easy difficulty setting to unlock the "Big Head", "Ricochet", "Head Shot", and "Ricochet All" cheat options. The remaining cheat options can be unlocked by completing the game under the other difficulty settings.
Glitch: Exceed Normal Ammo Maximum
Normally, all guns carry a nominal maximum of reserve bullets (i.e., MP40 carries 32 in the magazine and 160 rounds in reserve). You can exceed this maxima for your non-default guns by dying and restarting from a checkpoint.
The game will assume that you still carry the gun you previously had (i.e., MP40 in this example) and allow you to collect ammo for it even though you do not have the gun in your possession.
When you do choose to pick up the gun you've had on your previous play, you will find that you'll have more than the normal amount of ammo for that weapon.
This glitch has been verified for the PS2 debug version of the game on the following stages using the MP40 ('cause it's common folks): Dead In Her Sights, Raiding the Fortress, Last Bridge Standing, and Into The Heartland.
Russian campaign
On the first tank level in the Russian campaign, it is best to use first person view to shoot the Nazis that have Panzershrecks and MP-40s. The MP-40s cannot hurt you, but are annoying. If you use third person view, you will miss.
Teddy Bear
In the stage Surrender at Aachen (Western Front), you will be in an enemy occupied house right from the start. The small room directly across from where you start from has a small teddy bear you may acquire with no known effect.
The Rolling Pillar
Remember the first level, the first time you played, to get out of the trench, only to be killed by the rolling pillar? Get killed by that pillar 15 times in a row, without getting any farther, to have the next level loaded to be the SAME level, but with the sky all bright clouds, and the ground white, with rolling pillars all over the level, constantly appearing. Also , your partner leading you around the level will say every once in a while, while jumping up and down in a glichy form, "Why did you have to get killed by all those pillars? Now were in pillar heaven!" The pillars don't hurt you though...
Unlimited Ammo
Pause the game and enter the following: R1, Circle, L1, Square, Circle, R1, Right, Right, Circle, Right.
20 story red apple with a lil'...