Best way to pass data between Windows and Linux

Hi all,

What is the best method to pass data between Linux and Windows?

I am building a Qt client app which resides in Windows (XP/7) and wants to communicate with backend written in C residing in a Linux Box through ethernet. The box is compact, low on resources and runs a trimmed down fedora 12 which restricts us from running a feature rich GUI in itself.

App is similar to ethereal/wireshark and requires constant data transfer. Encryption is also required on certain parts which deals with WPA keys etc.

Please suggest ways around which I can do this effectively. As our application requires precision to some level (best ethernet can provide) because it basically deals with delay, drop etc of tcp/udp data traffic, fastest way of communicating would be preferred.

Please let me know if any further clarifications are required.

TIA
Deepak