Making an editable spreadsheet using POI

This is my first time using POI in a production app. I am reading a predefined template from a web share and filling it with data obtained from a database. My question and my problem is I can display the excel sheet easily enough, hower when the spreadsheet pops up, it is a readonly sheet. Is there a way to read a sheet and allow data served from a web application to fill it up. Here is what I have

Open the file:

String templatepath = ConfigurationManager.getAppProperty("URL");
filename = templatepath + template;      
      try {
                        
            POIFSFileSystem fs = new POIFSFileSystem(new FileInputStream(filename));
            book = new HSSFWorkbook(fs);                  
            } catch (FileNotFoundException fnfe) {
                  throw fnfe;
            } catch (IOException ioe) {
                  throw ioe;
            }

heres how I display the sheet to the user....

public void display(HttpServletResponse res) throws Exception {
            try {

                  // the following will download excel file within a stream and pop up a "save as" dialog to
                  // save the data...... see http://www.onjava.com/pub/a/onjava/excerpt/jebp_3/index3.html                  
                  // res.setContentType("application/octet-stream");
                  // res.setHeader("Content-disposition", "attachment;filename=Report.xls");

                  // the following will cause browser to display result with excel plug-in
                  res.setContentType("application/x-msexcel");

                  // the following will cause browser to display result with excel plug-in (within IE only)
                  //res.setContentType("application/vnd.ms-excel");

                  OutputStream os = (OutputStream) res.getOutputStream();
                  BufferedOutputStream bos = new BufferedOutputStream(os);

                  writeWorkBook(bos);
                  bos.close();
                  os.close();
            } catch (Exception e) {
                  throw e;
            }

public void writeWorkBook(BufferedOutputStream bos) throws IOException {

            try {
            book.write(bos);
            } catch (IOException ioe) {

            }

and finally here is a sample of how I want to prefill with data retrieved from our database..

HSSFSheet sheet = book.getSheet("TDP");
HSSFRow row = sheet.getRow(4);
HSSFCell cell = row.getCell(Short.parseShort("1"));
cell.setCellValue(model.getFieldName());

no matter what I do, when the spreadsheet comes up it is always a readonly copy, I really need something that is editable. Anybody have any ideas???