Converting A table (DataSet) to Xml in Asp.net

LoginDetails objLogin = (LoginDetails)Session["LoginDetils"];
                int _BranchID = Convert.ToInt32(objLogin.BranchID.ToString());
                int _FinancialyearID = Convert.ToInt32(objLogin.FinancialyearID.ToString());
                int _WarehouseID = Convert.ToInt32(objLogin.WarehouseID.ToString());
                DateTime Date = Convert.ToDateTime(txtDate.SelectedDate);
                Dashboard objInvSalesDashboard = new Dashboard();
                DataSet Ds = new DataSet();

                Ds = objInvSalesDashboard.DailyPurchaseReport(_FinancialyearID, _BranchID, _WarehouseID, Date);
                StreamWriter xmlDoc = new StreamWriter(Server.MapPath("~/images/Testdo.xml"), false);
                Ds.WriteXml(xmlDoc);
                xmlDoc.Close();


                string strFullPath = Server.MapPath("~/images/Testdo.xml");
                string strContents = null;
                System.IO.StreamReader objReader = default(System.IO.StreamReader);
                objReader = new System.IO.StreamReader(strFullPath);
                strContents = objReader.ReadToEnd();
                objReader.Close();

                string attachment = "attachment; filename=test.xml";
                Response.ClearContent();
                Response.ContentType = "application/xml";
                Response.AddHeader("content-disposition", attachment);
                Response.Write(strContents);
                Response.End();

<NewDataSet>
<Table>
 <Date>07/01/2012</Date>
 <Billno>27</Billno>
 <PatientName>v1</PatientName>
 <ItemName>PB32 POWERBOR MACHINE - 240V</ItemName>
 <BillAmount>1000.000000</BillAmount>
 </Table>
<Table>
 <Date>07/01/2012</Date>
 <Billno>27</Billno>
 <PatientName>v1</PatientName>
 <ItemName>PB32 POWERBOR MACHINE - 240V</ItemName>
 <BillAmount>600.000000</BillAmount>
 </Table>
 </NewDataSet>

<NewDataSet>
 <Table>
  <Billno=27  Date=07/01/2012  PatientName=v1> 
 
  <ItemName>PB32 POWERBOR MACHINE - 240V</ItemName> 
  <BillAmount>1000.000000</BillAmount> 
  <ItemName>PB32 POWERBOR MACHINE - 240V</ItemName> 
  <BillAmount>600.000000</BillAmount> 
 </Billno>

</NewDataSet>
 </Table>