Cheat mode:
Create a shortcut to the file "mgsvr" in the Metal Gear Solid folder. Right click the icon for the shortcut, select "Properties", and add -cheatenable to the end. Press [F12] during game play to activate God mode.

Hints:

Completing Variety Mission 13:
Knock down the giant soldier on the right (that enters first), before both of the soldiers get to the point when they stand still. While the first soldier is falling over, the second soldier will reach his post and stand still. The first soldier will get up, become confused, roar, and attack the second soldier. They second guy will get up and fight, finishing the mission for you.

Completing advanced mode level 3 for the Nikita:
Go down to the third step from the bottom. Face toward the bottom of the screen and fire. Guide the missile around the outside of the stage and to the back of the stage. Let the missile hit the wall behind the guard. This will kill the enemy and save time on time attack.

Easy record time on ninja level 3:
Note: Do this repeatedly until Snake is in the correct location; he may not always be there. As soon as you start, run down the hall without swinging the sword and hang to the left hard. Ignore the guard, as he will not be bothered unless you do not hang to the left. Once past the guard, run to the left, around the corner, and straight to see and kill Solid Snake. Repeat this as many times as needed until Snake is in this position. After he is dead, run straight to the goal and you should have a first place record.