platform independent set-up

Hi,

We are working on a project that requires a platform-independent collection of modules. For example, we currently have
aprototype version of a front-end running, developed with QT. I've also got postgreSQL running using CygWin. There is
noneed for 
network-functionality, everything should run on one machine, but we want to be able to transfer it completely
(includingdatabase) from WinNT to Linux and back. 
We also need speed in this application. That's why we prefer to code in C(++).

The question now is how to communicate from my front-end to the database and back? I don't know much about this part of
systems,but I guess that ODBC and JDBC are the kind of stuff I need. But I am not sure if they have what I need. I
don'tthink ODBC 
can run on Linux, or that there is a JDBC driver for (postgres on CygWin).

Could anyone assist me here?