I need to control them concurrently, and provide some interface where the results from one program can drive the input to the other program. I ask program A to do something, it gives me an answer; based on that answer, my Perl program decides what to tell program B to do. There will probably need to be some sharing of data between the two applications, but I think that can be accomplished through our Samba mount.

You could use a HTTP server and a client. This does not qualify as "simple", but it is quite tested and not too difficult to implement.

If the Win32 machines filesystem is visible to the unix box (via Samba or similar) then you could have the Win32 app create a Named pipe and the unix app can just open/read/write to/from that.

The nice things about this is that if the Win32 app creates the NP at a domain server, it can do so from any machine that can see the domain server and the unix app can run on any machine that can see that domain server. This indirection through a 3rd machine is rather easier to coordinate than ip.port combos.

Win32::Pipe allows (limited) access to the native Named Pipe apis from perl. The downside is that the implementation is a blocking API with no apparent mechanism for timeouts.

Back in the real world, Web services ARE a viable option here, if you are not looking for blinding speed.

I thinks fellow monks will bless web services as usable, in this context.