Thanks, Bear!
My experience with JavaScript is close to zero. I'm just trying to repair someone else's code and learn something along the way.
Unfortunately, now that I'm home using a Mac, I can't reproduce the problem -- it works fine in Safari using an XMLHttpRequest instead of ActiveXObject. But using IE earlier, I displayed the readyState before trying to get the responseXML, and it showed 4...
But in reviewing the link you provided, I noticed the following...
It is essential that the data returned from the server be sent with a Content-Type set to text/xml. Content that is sent as text/plain or text/html is accepted by the instance of the request object however it will only be available for use via the responseText property.
I was experimenting with all of this while my server was down for maintenance, so my html and xml files were just on my C-drive -- not a server. So my guess is that the Content-Type was messing things up. Does that make sense? Or am I still missing something with the readyState?