Help with Downloads

I have a LAN with 5 computers attached. On one of the machines I cannot open mail (yahoo, hotmail, squirrelmail) or download software. I can access Internet sites and move about through various pages, but it seems downloading does not work. This only happens on 1 of the connected machines, will work fine from the 4 others. I have already reloaded IE 6.0 and Windows 98 version 2. Any suggestions?

Thank you
Joe Doyle