FTP in Internet Explorer 6

We have a mixed Windows NT, 2000 and XP environment. All machines have Internet Explorer 6 with SP1 and all relevant MS patches yet many cannot use the FTP://. On one 2000 box, I can FTP to an FTP site and the other, I get “Page cannot be displayed.” I tried following MS’s article on the issue but it really doesn’t apply. I need all machines to have FTP ability through IE6. H E L P ! It doesn’t make any sense