/// <summary>
/// Copies values of up to 20 columns for a given row from the original sheet 
///   to the destination sheet
/// </summary>
/// <param name="origin">Worksheet object from which to copy from</param>
/// <param name="destination">Worksheet object to which to copy to</param>
/// <param name="row_from">Row number to copy from the origin to the 
///   desination</param>
public static void CopyWorksheetRow(Worksheet origin, Worksheet destination, 
    int row_from)
{
    // create an area of 1 row / 20 columns  (Note our sample only has 7 columns)
    Area selected_row = origin.CreateArea(row_from, 0, 1, 20);

    // out of that area extract only the cells 
    // with values (Note this will select that area of only 7 columns)
    Area populated_cells = selected_row.PopulatedCells;

    for(int x = 0; x < populated_cells.ColumnCount; x++)
    {
      destination.Cells[row_to_start_at,x].Value = populated_cells[0, x].Value;
      destination.Cells[row_to_start_at,x].Style = populated_cells[0, x].Style;
    }

    row_to_start_at++;
}

ExcelApplication xap = new ExcelApplication();
Workbook wb = xap.Open(Page.MapPath("datadoc.xls"));

Worksheet data_sheet = wb.Worksheets[0];
Worksheet filtered_datasheet = wb.Worksheets.CreateWorksheet("mysheet", 1);

// set up a loop to look throught the cells in column 6 (indexed as 5) from
//   rows 6 to 71
for(int x = 5; x < 71; x++)
{
    int cellval = int.Parse(data_sheet.Cells[x, 5].Value.ToString());

    // if the cells value matches our criteria 
    // call a function to copy this row onto a separate sheet.  
    // in my case I want to copy the rows where 
    // the volume of stock traded is under 300,000
    if(cellval < 300000)
    {
        CopyWorksheetRow(data_sheet, filtered_datasheet, 
            data_sheet.Cells[x, 5].RowNumber);
    }
}

//Save to disk on the server
xap.Save(wb, Page.MapPath("C:\\MyReports\\output.xls"));