Trouble reading iTunes XML feed

I am trying to read an XML feed from http://ift.tt/1tQL0Fb.

I want to access the fields like this:

<im:price amount="1.29000" currency="USD">$1.29</im:price>
<im:releaseDate label="December 31, 1960">1960-12-31T16:00:00-07:00</im:releaseDate>

Here is what I have done so far:

var xml = "http://ift.tt/1tQL0Fb";
XmlDocument doc = new XmlDocument();
doc.Load(xml);
XmlNodeList items = doc.SelectNodes("//entry");
foreach (var item in items) {
    // Do something with item.
}

No luck, though. items is null. Why? What am I doing wrong?