How to transfer the result to a dataset type

HI,
   I use Adomd.net to visit the sql server 2005 analyst service.  i
want the get a serializable result.
   Code seems like:

    AdomdCommand cmd = new AdomdCommand();
  ....
  System.Xml.XmlReader xr = cmd.ExecuteXmlReader();
  DataSet ds = new DataSet();
  ds.ReadXml(xr);

   // string strXml = xr.ReadInnerXml();
  // MemoryStream ms = new
MemoryStream( Encoding.Default.GetBytes(strXml) );
 // ds.ReadXml( ms );


now, the ds doesn't contain any data.
if use the second mothod, it re****t me that "the xml contains many
root element". I checked the xml , it contains many root element, such
as "schema" , "OlapInfo","Axes",.

So Is there a way to get a DataSet or DataTable  when querying the
cube?