Access your RetroArch directory; on Steam right click on RetroArch → Properties → Local Files → Browse

Download from https://buildbot.libretro.com/nightly/windows/x86_64/latest/ and extract the dll within into the subfolder of your RetroArch directory

Download https://github.com/libretro/libretro-core-info (click raw[raw.githubusercontent.com] and Save As) and put it into the subfolder of your RetroArch directory

Install BlueMSX standalone[bluemsx.msxblue.com] -- we only need this temporarily in order to copy files from the installation. From its installation directory (by default on a 64-bit system it will be `C:\Program Files (x86)\blueMSX`) copy the folders `Databases` and `Machines` and paste them into the subfolder of your RetroArch directory.

On other platforms, for example iOS, BlueMSX core is installed by default, but it will not work without the `Databases` and `Machines` directories from BlueMSX. You can copy these same folders you got over to the `system` directory on that platform’s respective RetroArch folder.

1. The original Metal Gear[retroachievements.org]
   
2. Metal Gear 2: Solid Snake[retroachievements.org]
   
3. List of MSX games supported by RetroAchievements[retroachievements.org]

If you want to get them to work with achievements, check out the Steam guide RetroAchievements for Dummies by Tuddywutwut. For Metal Gear you need the Japanese ROMs, and apply an English translation patch with a tool like Lunar IPS[www.romhacking.net]. Check the official forum topics for each of the games on RetroAchievements for the names and hashes of supported ROMs and links to the translation patches.