Metal Gear Solid Cheats

Create a file in notepad called mgs.bat
all the file should contain is (assuming you used default install):

cdprogra~1metalg~1
mgsi.exe -cheatenable

Save the file and run the game from that file.

when in game press:

F2 - god mode
F6 - observe mode
F5 - normal view mode
F7 - Quick level restart

Take a picture of the following locations using the camera to view hidden ghosts who are KCEJ development team members.
 
Name Location
Fujimura Elevator in the Comm Tower B complex
Fukushima Heliport; looking out to sea from cliff
Hirano Elevator in Comm Tower B; deep in the shaft of top level
Ishiyama Heliport top of building
Ito Inside elevator to tank hangar
Jerem Blaustein Sniper Wolf's corpse
Kaneda The mirror located in the Women's restroom
Kimura MG underground base; tip of Metal Gear 's railgun
Kinbara Dark area of stairs
Kitao Decoy Octopus (fake DARPA chief) corpse
Kobayashi Rock in canyon
Kobayashi Johnny Sasaki holding cell, near DARPA chief
Kojima Otacon lab; the picture frame to the right
Korekado Men's restroom
Kozyou Behind the watertank-like structure in the Canyon
Kutome Observation room
Makimura Hidden armory store room; behind the weakened wall
Matsuhana Hallway of corpses; outside Otacons lab
Mizutani When fighting Metal Gear
Mori Lowest point of elevator; Comm Tower B
Mukaide Reflection in wolfdog cave puddle
Muraoka Water in cargo dock
Nakamura In Meryl's blood pool; where she is sniped
Negishi Sewage waterfall
Nishimura Next to Baker's corpse
Okajima Maggots of the real DARPA Chef in cell
Onoda Where Baker is tied up
Sasaki Picture frames in the Commander's room
Sato Comm Tower A; roof destroyed by Hind D missiles
Scott Dolph Deep down in the dark from the walkway between Comm Towers A and B
Shigeno Heliport,security caera by staircase
Shikama Electric floor
Shimizu Wolf dog cave; first crawling point
Shinkawa Deep in Sniper Wolf's hallway behind the second pillar
Sonoyama Torture machine
Takade Ninja room; glass atedga
Tanaka Heliport; sleeping soldier
Tougo End of boiler room; in Blast Furnace with the steam
Toyota Container in the middle of Raven's warehouse
Uehara Edge of elevator; where the ravens are
Yamashita Tip of nuke warhead in nuke storage room
Yoshimura Dead end of air duct
Yoshioka Bridge on the third floor of the blast furnace

Cheat Mode:
Start the game with the 'mgsi.exe -cheatenable' command line. Then press the following keys during game-play
F2: Restore Energy
F4: Unlimited Ammunition (only at certain points)
F5: From Observe Mode Return to Normal view
F6: Observe Mode (camera can be moved throughout Level)
F7: Immediately restart Level with all items already collected
F8 - F12: Toggle alternate Graphics Textures

When you find Meryl on patrol in the office, she runs
to the women's bathroom. Follow Meryl into the Women's bathroom
and reach the last stall in under five seconds. Meryl will be
caught with her pants down during an FMV sequence.
Look in the vent just before the DARPA chief (Decoy Octopus) to
see Meryl doing sit-ups. Leave the vent and re-enter and she will
be doing one-armed pushups. Repeat and she will be doing leg stretches
on the wall. Repeat one more time and she will be doing the leg
stretches while pantless.
Cheats: Weapons, Items, Characters, Locations, Gitches...

Reach area B2 of the tank hanger. At the end of the hallway to the right of the door where you fight revolver is a secret room that is entered after using C4 explosive. In the room are card 4 and card 6 doors. The camera is in the room behind the card 4 door. Use the camera to take pictures to see various extras, such as the faces of the development team.