>software

Well, you might need DOS and a packet driver for your ethernet card, a
TCP/IP stack (trumpet ?), and a compiler that comes with libraries
suitable for socket level TCP/IP (streams, not UDP). Since there are
applications that run under DOS like this (ex: Lynx text mode www browser)
you should have no trouble locating the parts. The DOS license would be
the most interesting part imho. If you reach 4MB RAM needed to run and
1.5MB ROM or flash then consider embedded Linux seriously. The TCP/IP
stack will consume a lot of memory anyway so you might need it. I do not
know if a DOS machine can stand up to 115K, processing, and TCP/IP
continuously.

hope this helps,

Peter

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