Exportar DataSet a Excel

public void exportToExcel(DataSet source, string pArchivo)
    {
        System.IO.MemoryStream o = new System.IO.MemoryStream();
        System.IO.StreamWriter excelDoc;

        excelDoc = new System.IO.StreamWriter(o);//fileName);
        const string startExcelXML = "<xml version>\r\n<Workbook " +
              "xmlns=\"urn:schemas-microsoft-com:office:spreadsheet\"\r\n" +
              " xmlns:o=\"urn:schemas-microsoft-com:office:office\"\r\n " +
              "xmlns:x=\"urn:schemas-    microsoft-com:office:" +
              "excel\"\r\n xmlns:ss=\"urn:schemas-microsoft-com:" +
              "office:spreadsheet\">\r\n <Styles>\r\n " +
              "<Style ss:ID=\"Default\" ss:Name=\"Normal\">\r\n " +
              "<Alignment ss:Vertical=\"Bottom\"/>\r\n <Borders/>" +
              "\r\n <Font/>\r\n <Interior/>\r\n <NumberFormat/>" +
              "\r\n <Protection/>\r\n </Style>\r\n " +
              "<Style ss:ID=\"BoldColumn\">\r\n <Font " +
              "x:Family=\"Swiss\" ss:Bold=\"1\"/>\r\n </Style>\r\n " +
              "<Style     ss:ID=\"StringLiteral\">\r\n <NumberFormat" +
              " ss:Format=\"@\"/>\r\n </Style>\r\n <Style " +
              "ss:ID=\"Decimal\">\r\n <NumberFormat " +
              "ss:Format=\"0.0000\"/>\r\n </Style>\r\n " +
              "<Style ss:ID=\"Integer\">\r\n <NumberFormat " +
              "ss:Format=\"0\"/>\r\n </Style>\r\n <Style " +
              "ss:ID=\"DateLiteral\">\r\n <NumberFormat " +
              "ss:Format=\"mm/dd/yyyy;@\"/>\r\n </Style>\r\n " +
              "</Styles>\r\n ";
        const string endExcelXML = "</Workbook>";

        int rowCount = 0;
        int sheetCount = 1;
        /*
       <xml version>
       <Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet"
       xmlns:o="urn:schemas-microsoft-com:office:office"
       xmlns:x="urn:schemas-microsoft-com:office:excel"
       xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet">
       <Styles>
       <Style ss:ID="Default" ss:Name="Normal">
         <Alignment ss:Vertical="Bottom"/>
         <Borders/>
         <Font/>
         <Interior/>
         <NumberFormat/>
         <Protection/>
       </Style>
       <Style ss:ID="BoldColumn">
         <Font x:Family="Swiss" ss:Bold="1"/>
       </Style>
       <Style ss:ID="StringLiteral">
         <NumberFormat ss:Format="@"/>
       </Style>
       <Style ss:ID="Decimal">
         <NumberFormat ss:Format="0.0000"/>
       </Style>
       <Style ss:ID="Integer">
         <NumberFormat ss:Format="0"/>
       </Style>
       <Style ss:ID="DateLiteral">
         <NumberFormat ss:Format="mm/dd/yyyy;@"/>
       </Style>
       </Styles>
       <Worksheet ss:Name="Sheet1">
       </Worksheet>
       </Workbook>
       */
        excelDoc.Write(startExcelXML);
        excelDoc.Write("<Worksheet ss:Name=\"Sheet" + sheetCount + "\">");
        excelDoc.Write("<Table>");
        excelDoc.Write("<Row>");
        for (int x = 0; x < source.Tables[0].Columns.Count; x++)
        {
            excelDoc.Write("<Cell ss:StyleID=\"BoldColumn\"><Data ss:Type=\"String\">");
            excelDoc.Write(source.Tables[0].Columns[x].ColumnName);
            excelDoc.Write("</Data></Cell>");
        }
        excelDoc.Write("</Row>");
        foreach (DataRow x in source.Tables[0].Rows)
        {
            rowCount++;
            //if the number of rows is > 64000 create a new page to continue output

            if (rowCount == 64000)
            {
                rowCount = 0;
                sheetCount++;
                excelDoc.Write("</Table>");
                excelDoc.Write(" </Worksheet>");
                excelDoc.Write("<Worksheet ss:Name=\"Sheet" + sheetCount + "\">");
                excelDoc.Write("<Table>");
            }
            excelDoc.Write("<Row>"); //ID=" + rowCount + "

            for (int y = 0; y < source.Tables[0].Columns.Count; y++)
            {
                System.Type rowType;
                rowType = x[y].GetType();
                switch (rowType.ToString())
                {
                    case "System.String":
                        string XMLstring = x[y].ToString();
                        XMLstring = XMLstring.Trim();
                        XMLstring = XMLstring.Replace("&", "&");
                        XMLstring = XMLstring.Replace(">", ">");
                        XMLstring = XMLstring.Replace("<", "<");
                        excelDoc.Write("<Cell ss:StyleID=\"StringLiteral\">" +
                                       "<Data ss:Type=\"String\">");
                        excelDoc.Write(XMLstring);
                        excelDoc.Write("</Data></Cell>");
                        break;
                    case "System.DateTime":
                        //Excel has a specific Date Format of YYYY-MM-DD followed by 

                        //the letter 'T' then hh:mm:sss.lll Example 2005-01-31T24:01:21.000

                        //The Following Code puts the date stored in XMLDate

                        //to the format above

                        DateTime XMLDate = (DateTime)x[y];
                        string XMLDatetoString = ""; //Excel Converted Date

                        XMLDatetoString = XMLDate.Year.ToString() +
                             "-" +
                             (XMLDate.Month < 10 ? "0" +
                             XMLDate.Month.ToString() : XMLDate.Month.ToString()) +
                             "-" +
                             (XMLDate.Day < 10 ? "0" +
                             XMLDate.Day.ToString() : XMLDate.Day.ToString()) +
                             "T" +
                             (XMLDate.Hour < 10 ? "0" +
                             XMLDate.Hour.ToString() : XMLDate.Hour.ToString()) +
                             ":" +
                             (XMLDate.Minute < 10 ? "0" +
                             XMLDate.Minute.ToString() : XMLDate.Minute.ToString()) +
                             ":" +
                             (XMLDate.Second < 10 ? "0" +
                             XMLDate.Second.ToString() : XMLDate.Second.ToString()) +
                             ".000";
                        excelDoc.Write("<Cell ss:StyleID=\"DateLiteral\">" +
                                     "<Data ss:Type=\"DateTime\">");
                        excelDoc.Write(XMLDatetoString);
                        excelDoc.Write("</Data></Cell>");
                        break;
                    case "System.Boolean":
                        excelDoc.Write("<Cell ss:StyleID=\"StringLiteral\">" +
                                    "<Data ss:Type=\"String\">");
                        excelDoc.Write(x[y].ToString());
                        excelDoc.Write("</Data></Cell>");
                        break;
                    case "System.Int16":
                    case "System.Int32":
                    case "System.Int64":
                    case "System.Byte":
                        excelDoc.Write("<Cell ss:StyleID=\"Integer\">" +
                                "<Data ss:Type=\"Number\">");
                        excelDoc.Write(x[y].ToString());
                        excelDoc.Write("</Data></Cell>");
                        break;
                    case "System.Decimal":
                    case "System.Double":
                        excelDoc.Write("<Cell ss:StyleID=\"Decimal\">" +
                              "<Data ss:Type=\"Number\">");
                        excelDoc.Write(x[y].ToString());
                        excelDoc.Write("</Data></Cell>");
                        break;
                    case "System.DBNull":
                        excelDoc.Write("<Cell ss:StyleID=\"StringLiteral\">" +
                              "<Data ss:Type=\"String\">");
                        excelDoc.Write("");
                        excelDoc.Write("</Data></Cell>");
                        break;
                    default:
                        throw (new Exception(rowType.ToString() + " not handled."));
                }
            }
            excelDoc.Write("</Row>");
        }
        excelDoc.Write("</Table>");
        excelDoc.Write(" </Worksheet>");
        excelDoc.Write(endExcelXML);
        excelDoc.Close();
        Response.AddHeader("Content-Disposition", "attachment; filename=" + pArchivo + ".xls");
        Response.ContentType = "application/vnd-excel";
        Response.BinaryWrite(o.GetBuffer());
        o.Close();
    }