To unlock all of the Snake vs. Monkey missions on Disc 2, first play Disc 1. When starting a new game on Disc 1 and are asked which Metal Gear Solid game you like, select option 4, I like MGS!. When the game starts, save it as soon as you can. Take out Disc 1 and insert Disc 2. Go to Snake vs. Monkey and all of the missions should now be unlocked instead of having ????? in their place. Doing this also unlocks the Demo Theater on Disc 1 and the Secret Theater on Disc 2, along with the Duel option on Disc 2.