Internet Explorer 6 is having a problem with displaying atom feed documents which's mime type is "application/atom+xml". The browser attempts to download the file instead of rendering it. Simply this happens because browser does not accept or recognize the mime type.
A simple hack can be done to avoid this issue from the server side. That is changing the mime type to appication/xml or text/plain, only if the user agent is IE6 in the HTTP header. Changing the mime type will not fix the problem but at least the browser will display the raw XML content.
The back end application or the server can be configured to send the correct mime type to the relevant browser by looking at the User-Agent header in the HTTP request.