you are both missing the point here, what use is it hosting a ftp server if no-one on the internet can access it? His router wont forward ports except if he sets it up to do so, or change it to bridged mode so that the server makes a pppoe connection.
1. change router to bridge mode, let server dialup to interner
2. set router up to forward ports to server, this however requires setting fixed ports on both router and the ftp server you have. Its also diffferent for every brand router you get, even different models differ from one brand. Not the easiest way, but definitly the safer way.