Cannot Get Data From REST URL

I thought this would be easy. The United States Geological Survey (USGS) now has a way of getting stream flow data from a REST URL. There are different parameters that can be passed, based on which river gauge is desired, which parameter (ie: water temp, water level), and how many days requested. Below is one such URL:

[URL]

If you access this URL directly in a browser, you get XML data. I thought this would be easy to get through some simple Javascript. Here is my code:

Code:
var xmlhttp = null;
if (window.XMLHttpRequest) {
xmlhttp = new XMLHttpRequest();
if ( typeof xmlhttp.overrideMimeType != 'undefined') {

[Code].....

I also tried dojox's window.name method. That was an adventure. I did what the example told me to do...assigning the call to "deferred". I did get the return XML, but the only way I could see it was to assign it to a DIV. I found no way to assign it to a variable for later processing.