If the school does have a firewall, then the only thing i can think of is changing port on your ftp-server to like 80 (http) and connect threw that, coz if there is a firewall it's blocking port 21 (ftp)
If the school doesn't have port 21 blocked.. (try
ftp://ftp.cdrom.com/ ) to check... if OK, then we can start bugtracking your NAT.