// Writting
XmlDocument xmlDoc = new XmlDocument();

XmlNode nodeItems = xmlDoc.CreateNode("element", "Items", "");

foreach (ListViewItem item in ListView.Items)
{
 XmlNode nodeItem = xmlDoc.CreateNode("element", "Item", "");

 XmlNode nodeFind = xmlDoc.CreateNode("element", "Find", "");
 nodeFind.InnerText = "...";

 XmlNode nodeReplace = xmlDoc.CreateNode("element", "Replace", "");
 nodeReplace.InnerText = "...";

 nodeItem.AppendChild(nodeFind);
 nodeItem.AppendChild(nodeReplace);
 nodeItems.AppendChild(nodeItem);
}

xmlDoc.AppendChild(nodeItems);

xmlDoc.Save(saveFileDialog.FileName);

<Items>
  <Item>
    <Find>a1</Find>
    <Replace>b1</Replace>
  </Item>
  <Item>
    <Find>a2</Find>
    <Replace>b2</Replace>
  </Item>
</Items>    

// Reading
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(openFileDialog.FileName);

XmlNode nodeItems = xmlDoc.FirstChild;

foreach (XmlNode nodeItem in nodeItems)
{
 string strFind = nodeItem.FirstChild.InnerText;
 string strReplace = nodeItem.LastChild.InnerText;
}