arch13 managed to get in though, so it doesn't seem like its blocked, if its not i'd say he'd have to setup the server to use PASV , thats generally why it hangs on listing.
also theres a control port and an ftp port, 20,21 normally
try filezilla over at sourceforge its free and has both client and server, you can limit the ports it uses, as well as which to use.
and also you be setup the firewall to forward both the control port and the ftp port.
typically with NAT youll need PASV mode set on the client
i have adelphia and pacbell and neither blocks ftp, in my area, theres no harm in trying and making sure that the firewall is setup correctly.
switch your firewall off or set it as DMZ to the machine with the ftp server and go to
http://www.grc.com and run a port scan with his probe tool, it should show up then, keep the ftp server on the standard ports for the test, make sure you disable dmz or switch the firewall on after the test
if it doesnt detect it and you are sure the firewall is off or DMZ is correct, then the isp is likely blocking you, if it does find open ports you can try that,