If you find yourself needing to upload files to our FTP site from behind a firewall you'll need to use a client that supports "passive" mode. Anyone knowing of such a program is asked to let the rest of us know.
For sport I installed Internet Explorer 5.5 beta today. Under advanced options the innovative folks as Microsoft have added a new checkbox "Use Passive FTP for compatibility with some firewalls and DSL modems". I don't recommend running the beta unless you are feeling particularly lucky, but when 5.5 is finally released this should probably be the canonical solution to the problem Guy describes.