I'm working with a client that needs a way to publish data from some
Excel spreadsheets and subscribe to those data changes in other
spreadsheets. Users on the Internet (outside the firewall) should be
able to publish some cells in their workbook so that other users see
their updates as they happen (a few seconds delay is ok, but I'd like
to avoid a polling architecture).

My recent experience is all C#/.NET, so I considered a .NET plugin that
would use Remoting (a TCP/IP wrapper) to do two-way communication with
a server. But I hear that .NET addins have problems. I'd like to
support at least back to Excel 2002 and prefer not to require the .NET
runtime.

So, it looks like I'm using VB6 or Delphi to build the addin. How can
I communicate with the server, given that I need to push data up to the
server and push from the server back to the client? I'm an experienced
C++ and C# developer with enough TCP/IP & sockets experience to prefer
a higher level network layer.

Some browsing in this group uncovered RTD servers, but I'm not sure if
they are applicable to my problem.

Thanks!