Level Passwords:

Enter any of the following passwords on the password screen to start from that level:

Level 2 - FCHTRMNS
Level 3 - HSDSHSBS
Level 4 - MXNMSNNG
Level 5 - THXBXSCK
Level 6 - NNTNDWNY
End Level - NFNTMMDD

View Ending
Enter the following codes at the Password screen....
NFNTMMDD
You should then see the ending movie

Have All Weapons
Input the following password:
LLWPNSDD

Infinite Ammo
Input the following password:
NFNTMMDD

Invincibility
To start the game with with invincibility, enter the following code on the password screen.
LVFRVRDD

You can now either start from the beginning or enter a level code