Well there are many ways of doing this, you can use XmlReader to read the
XML doc or you can use XPath to get the nodes that you want. Depending on
the your situation you should choose the one that suit you best.

XPath is the most convenient - imho, so I would do:

XmlNodeList surveyList = xmlDoc.SelectNodes("//UserData/Survey");
foreach (XmlNode surveyNode in surveyList)
{
   Console.WriteLine(surveyNode.Attributes["ID"].InnerText);
   XmlNodeList userList = surveyNode.SelectNodes("User");
   foreach (XmlNode userNode in userList)
   {
       Console.WriteLine(" " + userNode.Attributes["ID"].InnerText);
   }
}

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Victor Hadianto
http://www.synop.com/Products/SauceReader/