> how can the installer on MACHINE_B detect it as an absolute path?
>

Oh and the installer does not need to detect anything here... the FBServer
will resolve this path relative to it's position.

If you are setting up (installing) to many network setups like this, you
need to have a component setup where the server and database are installed
as a separate "custom" install and chosen only once per LAN setup. The
default setup will only install your application and the FB client
libraries.
Alan