Now that we have a machine running, we want to install EarthSiege 2 itself.
Obtain the 1.11 ISO from https://archive.org/details/sierra-earth-siege-2, you will need the EarthSiege2_Freeware_GoldGames_1r11_dataOnly.iso file. Do not use the 1.0 version, it will not run on modern Windowses. Also, do not use the installer from sierrahelp.com since it installs the 1.0 binaries that won't work. Apparently they never heard of the 1.11 patch?! (TODO for me: either brew my own installer package or contact the people at sierrahelp to update theirs)
Mount the ISO in your VM
In VirtualBox you can mount it using the Devices menu
If you're on a physical machine, use Virtual Clone Drive to mount the ISO (since the vendor of this tool also used to sell software that is related to piracy, I can't link to it for German law reasons)
Burn the ISO to a CD-ROM. In theory, you can also use the _withAudio.iso file for this to have background sounds in play, but burning support for raw ISOs including ECC information is sketchy at best and I haven't tried / tested this.
Run d:\setup.exe and follow through with a full installation. Ideally, the test that runs as part of the setup should run without a hitch - if there are errors, something earlier has gone bonkers
TODO: Insert instructions on how to achieve a no-cd install here
Open Windows Explorer, navigate to c:\sierra\es2 and set the compatibility quirks (roughly translated, I'm German)
Run in Windows 95 mode
Run with 256 colors
Deactivate Visual Designs
Deactivate Desktop Skins
Disable high DPI scaling
Run as Administrator
Have fun!