To get unlimited lives and unlimited Super Machinegun, go to "Main Menu" > "Arcade Game" and press UP(2), DOWN(2), LEFT, RIGHT, LEFT, RIGHT, B, A. Note: Enabling this cheat will disable the earning of Achievements.
ACHIEVEMENT - HOW TO UNLOCK Good Start (10 points) - Beat level 1 in under 3 minutes. Two Levels (10 points) - Beat level 2 while playing an Xbox Live CO-OP game. Three Levels (15 points) - Beat level 3 in Single Player or Multi-Player mode. Four Levels (20 points) - Beat level 4 in Single Player mode. Five Levels (30 points) - Beat level 5 in Single Player or Multi-Player mode. Armory (15 points) - Collect 5 different weapon types. Good Score (10 points) - Reach level 2 with a score of 100,000 or more. Team Players (20 points) - Score 300,000 points in an Xbox Live CO-OP game, while still alive. Shot Down (15 points) - Destroy the helicopter without dying once. Elite Soldiers (10 points) - Both players possess a Spread Gun at the same time at some point in the game. Endurance (10 points) - Both players must complete level 1 without losing lives in an Xbox Live CO-OP game. Master (35 points) - Beat the game using only 1 credit.