Turns out the 1.75b CD has a WIN31 directory with a separate installer for the 16-bit version. There's also a 16-bit evaluation installer that I couldn't find anywhere on the web.
I thought I'd have to go further back than 1.75a. This zip only has an NWC32.EXE, which crashes with a MSVFW32.DLL error (I have win32s installed), but the readme says it should work on Windows 3.1. This at least gives me some clues. Maybe if I can find my optical drive I'll see if there are other versions on my 1.75 CD.
Does anyone know where I can get a 16-bit version of NWC? I tried archive.org and the wayback machine but no luck.
Yes, I understand how quixotic this is. I've been spending time in Win 3.1 and I'm finding the minimalism extremely soothing. I've been using NWC for over 15 years and I know how far it's come.
I'm a registered user of the latest version, and I also still have my 1.75 cd in the jewel case, so if the registration code didn't change too much I'm hoping I can just unlock an ancient evaluation version.
