When the game has loaded select your control method at the options screen as usual. Instead of going to {Start Game} press 'ESC'. Wait for the high score chart with the picture of the T-1000 to appear. As soon as the last digit is printed on the high score chart (the last 0 on the 10000, in 10th place), click the left mouse button (or the joystick fire button if that's plugged in to port one). Note you must click the button 0.19 seconds after the last digit on the high score chart has been printed on the screen. If you take longer, or click before the last digit is printed, the cheat will not work, so precise timing is required.
If you find this difficult there is an alternative. Hold down the fire button or left mouse button at the high score table until it is finished. This won't always work though.
Go back to the options screen. If you can see the picture of Arnie, but no options are displayed, then the cheat worked. Left click on the mouse (or joystick) to move on. Click again to skip the high score display. If you allow the high score chart to be printed again the game may mess up. Start the game.
If you didn't get it to work restart the whole procedure.
Once you've started playing you'll notice that a gunpowder and energy reading is displayed for player two even though he isn't active. Now pause the game (press 'P' not 'F1') and type in all the function keys in order F1, F2, F3, F4, F5, F6, F7, F8, F9, and F10 and you should skip the level you are presently playing. This cheat is for one player only.
Enter your intials as "PMT" on the high score table, and then you can skip levels by pressing F10 when the game is paused.