Odd. The Internet Explorer error "Page Not Found" usually relates to the fact that your computer was unable to communicate with the remote server (in this case
http://dmoz.org/ ).
Have all 3 PCs been attached to the same ISP? (It could be a proxy issue - even if you don't have one set, your ISP could have a "seamless proxy").
Have you tried using Netscape, Mozilla or Opera (under heavy loads the ODP server can be slow to respond to CGI queries - and, hence, IE may time out: the others are a bit more accepting with overloaded servers).
If you post with your URL and the category you submitted to, and editor will be able to check if your submission did, in fact, reach us.
If you could post with a brief description of your set-up ("Internet Explorer 6 on Windows 2000 Professional using XYZ ISP") it may help us track down problems like this. We are aware that a number of people have experienced similar problems (usually they get a "Unable to determine your IP address" message - but their submission does reach us OK), but apart from the common factor of Internet Explorer (we don't even know which version), we've been unable to pinpoint exactly what's going wrong.