I progressed a little,

I specified in the delphi dbexpress
database localhost:mydatabasealias
user sysdba
password ****

now I see in the firebird.log --

MINICOSMOS (Server) Tue Sep 16 12:53:26 2008
SERVER/process_packet: connection rejected for NIGHTHAWK.-1.-1

why doesn't it uses the user and password I give it, in the connection
command?