You might be able to detect if there is already a Firebird/Interbase
server listening on port 3050 by doing

telnet localhost 3050

If the response is "could not open connection to host" then that
suggests there's nothing listening on that port. I don't have
firebird installed here, but I just tried with postgresql, and it
doesn't return the above error because postgres is listening on port 5432.

However, certainly Windows Vista Home is so brain-dead that Microsoft
disables the telnet client by default. You need to go to Control
Panel/Programs and enable it. And then it takes a few minutes for the
enabling to take place. Maybe other versions of Vista have it enabled
by default.

Bernard