That should be possible.
Diablo officially supports multiplayer over UDP/IP via battle.net, IPX over LAN, modem, or serial. You probably don't have (or want to use) modem or serial. Recent versions of Windows dropped IPX support. That leaves you with UDP/IP over the Internet, or some unofficial but well-tested approaches. Starcraft gained the ability to offer UDP/IP over LAN, and swapping in the right files from a recent version of Starcraft can grant that ability to Diablo. You could also play over battle.net, but note that if you use a single public IP for both systems (common), then your router will need to support hairpin routing: letting an internal client try to access the public IP, and redirecting that attempt back inside.
If you don't already have Diablo working on both systems (which, if you have lost your discs, could be the case), one way you could test this at no cost would be to test with one of the free Blizzard games that uses the same transport: Diablo Shareware or Starcraft 1 (non-remastered) should both work for this. Both are available at no charge, direct from Blizzard. Try to set up a Diablo Shareware game between the two systems. If you can get that to work, full Diablo should work too. If you can't, then you'll need to decide between not playing full Diablo or spending some time making it work.
Post edited July 20, 2019 by advowson
