uhh so many thngs going on here, sorry I'm not much around in this Forum so my answers are a little bit delayed.
@MoRetro
hmm no idea about VirtualBox. It's a 32Bit Machine, 1-2 GB Ram should be enough, network and so on I don't know.
Any particuallar reason to not use VMWare? I used VB before and found VMWare much more reliable and compatible, especially because I use Linux as host VirtualBox is REALLY Slow
About the missing "Interface" unit, that means that is a Lazarus/LCL application, not meant to be edited by the FP-Editor (Even possible of course). (That also means the Mines program can be compiled for Windows and Linux also, and look rather the same like:
https://blog.alb42.de/2015/12/23/bring-it-together/ )
You need the path to the LCL units.
If you use the command line compiler it should work out of the Box
fpc Mines.lpr
if you also want to use the FP-Editor you have to add the path to LCL units to the searchpath of the Editor. Menu Options -> Directories Tab "Units"
add the two directories:
FreePascal:lcl
FreePascal:lcl/*
@emufan:
hmm that means it's a rather old source, systemvartags is obsolete and not needed anymore. (You could try to just comment it out, but I'm not sure if it will work then, many changes are made since this version)