The first option is very useful when creating new messages from scratch. However, the method I show here is not very useful for complex messages, because it would be very hard to maintain an read. For those scenarios, I really recommend Scott Colestock's option of creating messages from embedded resources in .NET assemblies; it's a much better option.

Here's some very small, yet useful piece of code to accomplish these tasks:

//
// XmlHelper.cs
//
// Author:
//    Tomas Restrepo (tomasr@mvps.org)
//

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

using Microsoft.XLANGs.BaseTypes;

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

using Microsoft.XLANGs.BaseTypes;

namespace Winterdom.BizTalk.Util
{
   /// <summary>
   /// Helper BizTalk class to deal with XML Based
   /// messages
   /// </summary>
   public class XmlHelper
   {
   
      /// <summary>
      /// Creates a typed BizTalk message
      /// out of a string containing valid XML.
      /// </summary>
      /// <remarks>
      /// This does not validate the message at all.
      /// </remarks>
      /// <param name="xml">XML content</param>
      /// <returns>The BizTalk Message</returns>
      public static XmlDocument CreateMessage(string xml)
      {
         XmlDocument doc = new XmlDocument();
         doc.LoadXml(xml);
         return doc;
      }
      
      /// <summary>
      /// Returns a string containing the XML from the message
      /// </summary>
      /// <param name="part">Message</param>
      /// <returns>The xml</returns>
      public static string GetMessageXml(XLANGPart part)
      {
         Stream s = (Stream)part.RetrieveAs(typeof(Stream));
         using ( StreamReader reader = new StreamReader(s) ) {
            return reader.ReadToEnd();
         }
      }
   
   } // class XmlHelper
   
} // namespace Winterdom.BizTalk.Util