var testcaseiterator = xmlDoc.getElementsById("tc").childNodes;
The rest of the code looks okay.
for(i=0; i < testcaseiterator.length; i++)
{
document.write("<tr><td>");
document.write(testcaseiterator[i].getAttribute('name'));
document.write("</td></tr>");
}
document.write("</table>")
You will also have to edit the 5th line of the XML,
<TestCase id ="tc" name="Visit all buttons [in region Button: Navi 0]">
This will only work if you XML in your DOM structure.