Need help: using "lsnrctl" and connecting through a firewall

I'm a beginner as Oracle manager (though I know many about theory), and a little bit lost with all that documentation where I can never find what I'm looking for...
Two problems in one :

1. I need to access to an Oracle Server (7.3.2) named "scotty" in a private network from a machine named "jenny" in another network but this one is connected to the Internet. Of course there's a firewall between the two... I have total control upon the machines, fiwewall, and so on, so it should work just fine ! I temporarily put the server, scotty, on the same network as jenny : the latter can connect without any problem, so the files LISTENER.ORA on the server and TNSNAMES.ORA ont he other machine I tried to put another machine on a completely different private network : no problem to connect to scotty either. So it seems to be a firewall problem : as soon as there's the firewall between the two machines, it doesn't work... so I opened it temporarily too : it still doesn't work, I get the message "ERROR: ORA-12203: TNS:unable to connect to destination". I checked all the points described in the explanation of this error message (explanation found on the CD-ROM "Support Notes" of Decemeber) : all is correct. Does anybody has any knowledge/experience with access through a firewall ?
2. I tried to check the listener with the program "lsnrctl" (though it should be running, as I can connect from any machine in the same network), but I can't get anything interesting from this badly documented tool : how does it works ? Most commands end by "TNS-01169: The listener has not recognized the password"... but which password ? If I try to change the password, I'm of course prompted for the current one, and as I don't know what it could be... and as nobody here ever set it, it should be a default one ?...