At the main menu hold Z and input the following:

Level Select:
Press C-Up, C-Right, C-Down, C-Left, Start

Unlimited Ammunition:
Press L, R, L, R.

Unlimited Armor:
Press Up, Right, Down, Left.

Free Buildings:
Press A, B, A, B.

Free Satellite:
Press B, C-Left, C-Down, A.