ok modificando così ce l'ho fatta:
Codice PHP:
                    <?php
                        error_reporting
(E_ALL);

                        if (
$_SERVER['REQUEST_METHOD'] == "POST") {

                            include 
'phpex/PHPExcel.php';
                            include 
'phpex/PHPExcel/Writer/Excel5.php';

                            echo 
date('H:i:s') . " Create new PHPExcel object
"
;
                            
$objPHPExcel = new PHPExcel();

                            echo 
date('H:i:s') . " Set properties
"
;
                            
$objPHPExcel->getProperties()->setCreator("Matteo");
                            
$objPHPExcel->getProperties()->setLastModifiedBy("Matteo");
                            
$objPHPExcel->getProperties()->setTitle("My library");
                            
$objPHPExcel->getProperties()->setSubject("My library");
                            
$objPHPExcel->getProperties()->setDescription("My library.");

                            echo 
date('H:i:s') . " Add some data
"
;
                            
$objPHPExcel->setActiveSheetIndex(0);
                            
$objPHPExcel->getActiveSheet()->SetCellValue('A1''Hello');
                            
$objPHPExcel->getActiveSheet()->SetCellValue('B2''world!');
                            
$objPHPExcel->getActiveSheet()->SetCellValue('C1''Hello');
                            
$objPHPExcel->getActiveSheet()->SetCellValue('D2''world!');

                            echo 
date('H:i:s') . " Rename sheet
"
;
                            
$objPHPExcel->getActiveSheet()->setTitle('Book');

                            echo 
date('H:i:s') . " Write to Excel2007 format
"
;
                            
$objWriter = new PHPExcel_Writer_Excel5($objPHPExcel);
                            
$objWriter->save("C:\\excel.xls");

                            echo 
date('H:i:s') . " Done writing file.\r
"
;
                            echo 
date('H:i:s') . " Peak memory usage: " . (memory_get_peak_usage(true) / 1024 1024) . " MB\r
"
;
                            echo 
date('H:i:s') . " Done.\r
"
;
                            
header('location:[url]http://62.94.208.157/book/index.php[/url]');
                        }
                    
?>
il problema è che salva il file sul server e nn sul pc che esegue la richiesta.