Thanks for the attachment, I'll try and make some sense of it- although I'm not very good with JS!
I think it's the XML HTTP Request part that isnt working.
It all works fine in all the major browsers except I.E.?
Not sure if you've seen my update but does it matter that I'm testing the site from my machine and not on a server? Does I.E. expect all the files (or the XML file at least) to be sitting on a server to make the XMLHttpRequest() work?
I'm testing this from my machine and not live. Could this be a reason why it's not working on I.E. because the files are on my computer and not on a server???
No, remember that if you make an xmlhttprequest you'r program isn't talking to the server but to the browser and then the browser makes a request to the server. But you forgot one way of making an xmlhttprequest object in IE as you can see in the file I've attached in my previous answer.
Now if a file doesn't exist the call's response will allways be htpp error 404 that's returned by response.statuscode