Peter asked how to display the XML for an Atom feed in a browser. In fact, when I was looking at the XML for feeds, I didn't try to display it in my browser (Opera), because Opera recognises it as a feed and wants to ask whether you want to subscribe, etc. I'm sure other browsers to much the same.
I actually opened up the Atom XML directly from the feed URL using the oXygen XML editor. You could equally use XML Spy or jEdit or any text editor that can download directly from a URL. Alternatively, you could use wget or curl to download the XML to your local PC, and then open the file in the editor of your choice.