You can extract an XmlDocument from the DataSet, and can then apply an XSL
transform on it.
And of course, you can do the converse, too.  examples:
http://samples.gotdotnet.com/quickstart/howto/doc/Xml/LoadXmlDocument.aspx

Have you tried this?

If you want to avoid the dataset and XSL on the DB-to-MQ path, there is an
FOR XML support in SQL2000, which allows you to extract whatever shape of
XML you like from a query.  You can do something like this:

     System.Xml.XmlTextReader xtr= null;
     System.Xml.XmlDocument doc= null;
     System.Data.SqlClient.SqlConnection dbconn= null;
     try {
       dbconn= GetDbConn();
       System.Data.SqlClient.SqlCommand cmd= new
System.Data.SqlClient.SqlCommand(strSQL, dbconn);
       cmd.Connection.Open();

       xtr = (System.Xml.XmlTextReader) cmd.ExecuteXmlReader();
       //xtr.WhitespaceHandling = System.Xml.WhitespaceHandling.None;
       doc = new System.Xml.XmlDocument();
       doc.Load(xtr);
       //do whatever you like here
     }
     ....

The FOR XML EXPLICIT can do basically what you describe here:

...but it is being done by SQL Server. The query strings can get pretty
ugly, though. See here for some help and examples:
http://www.topxml.com/sql/for_xml_explicit.asp

Regardless how you get it, once you have the XmlDocument you can transform,
serialize, whatever.

-D