InsertAfter

using System;
using System.IO;
using System.Xml;

public class Sample {

  public static void Main() {

    XmlDocument doc = new XmlDocument();
    doc.LoadXml("<book genre='novel' ISBN='1-861001-57-5'>" +

                "<title>Pride And Prejudice</title>" +

                "</book>");

    XmlNode root = doc.DocumentElement;

    //Create a new node.
    XmlElement elem = doc.CreateElement("price");
    elem.InnerText="19.95";

    //Add the node to the document.
    root.InsertAfter(elem, root.FirstChild);

    Console.WriteLine("Display the modified XML...");
    doc.Save(Console.Out);

  }
}

XMLAttributionCollection, Item

public class Sample
{
  public static void Main()
  {
     XmlDocument doc = new XmlDocument();
     doc.LoadXml("<book genre='novel' publicationdate='1997'> " +

                 "  <title>Pride And Prejudice</title>" +

                 "</book>");      

     XmlAttributeCollection attrColl = doc.DocumentElement.Attributes;

     Console.WriteLine("Display all the attributes for this book...");
     for (int i=0; i < attrColl.Count; i++)
     {
        Console.WriteLine("{0} = {1}", attrColl.Item(i).Name, attrColl.Item(i).Value);
     }         

  }
}

HTTP, BaseURL(Uniform Resource Indicator)

using System;
using System.IO;
using System.Xml;

public class Sample
{
  public static void Main()
  {
    //Create the XmlDocument.
    XmlDocument doc = new XmlDocument();
    doc.Load("http://localhost/baseuri.xml");

    //Display information on the attribute node. The value
    //returned for BaseURI is 'http://localhost/baseuri.xml'.
    XmlAttribute attr = doc.DocumentElement.Attributes[0];
    Console.WriteLine("Name of the attribute:  {0}", attr.Name);
    Console.WriteLine("Base URI of the attribute:  {0}", attr.BaseURI);
    Console.WriteLine("The value of the attribute:  {0}", attr.InnerText);

  }
}

Attributes collection

using System;
using System.IO;
using System.Xml;

public class Sample
{
  public static void Main(){

    XmlDocument doc = new XmlDocument();
    doc.LoadXml("" +
                "" +
                "");     

    //Create an attribute collection.
    XmlAttributeCollection attrColl = doc.DocumentElement.Attributes;

    Console.WriteLine("Display information on each of the attributes... \r\n");
    foreach (XmlAttribute attr in attrColl){
       Console.Write("{0}:{1} = {2}", attr.Prefix, attr.LocalName, attr.Value);
       Console.WriteLine("\t namespaceURI=" + attr.NamespaceURI);
    }
  }
}

XmlTextWriter & MemoryStream

private byte[] GenerateXXXXXML()
        {
            byte[] distBytes = new byte[1];

            using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
            {
                XmlTextWriter xtw = new XmlTextWriter(ms, Encoding.UTF8);
                xtw.Formatting = Formatting.Indented;
                xtw.WriteProcessingInstruction("xml", "version='1.0' encoding='utf-8'");
                xtw.WriteStartElement("PRODValidation");
                xtw.WriteAttributeString("xmlns", "http://www.XXX.com/PRODUCT/validate");
                
                // charge type
                xtw.WriteStartElement("Query");
                xtw.WriteAttributeString("name", "TABLENAME");
                xtw.WriteStartElement("Parameters");
                xtw.WriteStartElement("Param");
                xtw.WriteAttributeString("name", "");
                xtw.WriteAttributeString("value", "");
                xtw.WriteEndElement();
                xtw.WriteEndElement();
                xtw.WriteStartElement("Result");
                xtw.WriteStartElement("Status");
                xtw.WriteEndElement();
                xtw.WriteStartElement("AdditionalInfo");
                xtw.WriteEndElement();
                xtw.WriteEndElement();
                xtw.WriteEndElement();

                xtw.WriteEndElement();
                xtw.Flush();
                ms.Flush();
                distBytes = ms.ToArray();
                xtw.Close();
            }

            return distBytes;
        }

Copy File from remote location (HTTP, https, FTP..)

string RemoteFolder = @"http://yoursite.com/YourWebFolder/";
string RemoteFile = "yourfile.txt";
string url = RemoteFolder + RemoteFile;
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse();
StreamReader sr = new
StreamReader(webResponse.GetResponseStream(),Encod ing.ASCII);
string filecontent = sr.ReadToEnd();
StreamWriter sw = new StreamWriter("c:\mynewfile.txt");
sw.Write(filecontent);
sw.Flush();
sw.Close();
sr.Close();

XML DOM - Samples

<?xml version='1.0'?>

<bookstore xmlns="urn:newbooks-schema">

<book genre="novel" style="hardcover">

<title>The Handmaid's Tale</title>

<author>

<first-name>Margaret</first-name>

<last-name>Atwood</last-name>

</author>

<price>19.95</price>

</book>

<book genre="novel" style="other">

<title>The Poisonwood Bible</title>

<author>

<first-name>Barbara</first-name>

<last-name>Kingsolver</last-name>

</author>

<price>11.99</price>

</book>

</bookstore>

---

using System;
using System.IO;
using System.Xml;

public class Sample
{
  public static void Main()
  {

      XmlDocument doc = new XmlDocument();
      doc.Load("newbooks.xml");

      // Create an XmlNamespaceManager to resolve the default namespace.
      XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
      nsmgr.AddNamespace("bk", "urn:newbooks-schema");

      // Select and display all book titles.
      XmlNodeList nodeList;
      XmlElement root = doc.DocumentElement;
      nodeList = root.SelectNodes("/bk:bookstore/bk:book/bk:title", nsmgr);
      foreach (XmlNode title in nodeList) {
        Console.WriteLine(title.InnerXml);
      }

   }

}

CreateElement:
==============

using System;
using System.IO;
using System.Xml;

public class Sample
{
  public static void Main()
  {
    //Create the XmlDocument.
    XmlDocument doc = new XmlDocument();
    doc.LoadXml("<book genre='novel' ISBN='1-861001-57-5'>" +

                "<title>Pride And Prejudice</title>" +

                "</book>");

    //Create a new node and add it to the document.
    //The text node is the content of the price element.
    XmlElement elem = doc.CreateElement("price");
    XmlText text = doc.CreateTextNode("19.95");
    doc.DocumentElement.AppendChild(elem);
    doc.DocumentElement.LastChild.AppendChild(text);

    Console.WriteLine("Display the modified XML...");
    doc.Save(Console.Out);

  }
}

using System;
using System.IO;
using System.Xml;

public class Sample
{
  public static void Main()
  {
    //Create the XmlDocument.
    XmlDocument doc = new XmlDocument();

    //Create a document type node and 
    //add it to the document.
    XmlDocumentType doctype;
    doctype = doc.CreateDocumentType("book", null, null, "");
    doc.AppendChild(doctype);

    //Create the root element and
    //add it to the document.
    doc.AppendChild(doc.CreateElement("book"));

    Console.WriteLine("Display the modified XML...");
    doc.Save(Console.Out);
  }
}

Contains() XPath Function in MS DOM

<?xml version="1.0"?>

<!-- This file represents a fragment of a bookstore inventory database -->

<bookstore specialty="novel">

<book>

<Title>Beginning XML</Title>

<Publisher>Wrox</Publisher>

</book>

<book>

<Title>Professional XML</Title>

<Publisher>Wrox</Publisher>

</book>

<book>

<Title>Programming ADO</Title>

<author>

<first-name>Mary</first-name>

<last-name>Bob</last-name>

</author>

<datePublished>1/1/2000</datePublished>

<Publisher>Microsoft Press</Publisher>

</book>

</bookstore>



Add References, by selecting the Microsoft XML 3.0 check box.

Dim doc As MSXML2.DOMDocument
Dim nlist As MSXML2.IXMLDOMNodeList
Dim node As MSXML2.IXMLDOMNode

Set doc = New MSXML2.DOMDocument
doc.setProperty "SelectionLanguage", "XPath"
doc.Load "c:\books.xml"
Set nlist = doc.selectNodes("//book/Title[contains(.,'ADO')]")
MsgBox "Matching Nodes : " & nlist.length

For Each node In nlist
Debug.Print node.nodeName & " : " & node.Text
Next

Source : http://support.microsoft.com/kb/304265