private void Form1_Load(object sender, System.EventArgs e)
{
  XmlDocument doc = new XmlDocument();
  doc.Load(@"c:\sample2.xml");
  XmlNamespaceManager nsmgr1 = new XmlNamespaceManager(doc.NameTable);
  nsmgr1.AddNamespace("smpl","http://www.atmarkit.co.jp/xmlns/sample/shoseki/info");

  XmlNode writerNode1 = doc.SelectSingleNode("//smpl:著者[@id='writer302']",nsmgr1);
  XmlNode writerNameNode = writerNode1.SelectSingleNode("smpl:名前",nsmgr1);
  Trace.WriteLine(writerNameNode.InnerText);

  XmlNode writerNode2 = doc.SelectSingleNode("//smpl:著者[smpl:名前='森野大樹']",nsmgr1);
  XmlNode writerOrgNode = writerNode2.SelectSingleNode("smpl:所属",nsmgr1);
  Trace.WriteLine(writerOrgNode.InnerText);
}