So I just tried the launcher, and it gave me an error: "This program does not support the version of Windows your computer is running."
I'm running Windows XP SP3, 32-bit.
And before anybody starts a stupid flame war about "yur usyng old operatyng sistem, uprage to Wyndows 10, teh best operatyng sistem evar!",
I'll tell you that I have my XP 32-bit dual-booted with a Windows 7 64-bit. For all the games I like, but cannot run on XP (all six of them). However I only use that if I have to, and a Diablo 2 mod shouldn't be like that...
I do have all the .net frameworks installed up to 4 (including 4), and all the c++ redistributables up to 2015, and newest directx 9, of course.
EDIT: I just realized that I am technically running a Windows WEPOS / POSReady (essentially an XP SP3 that is supported by automatic updates up until 2019), which might be why the installer is b*tching. (but this is the very first time I came across that if it indeed is the source of the problem).