TCP/IP under Windows 3.1
Microsoft has a TCP/IP stack for Windows 3.11. The link to the download is in the main posting in the blog. It uses the NDIS2 driver of the emulated network card. It binds and will allow Internet access without needing a modem, although IE 5.01 still acts as if it needs a modem.
There are a few DOS TCP/IP stacks around. I dont have any right now, but I'll see if I can find one.