OK, I get it ! I corrected the metadata information in the wiki page (too spaces), that seems work. And I use this code :
<?php
// $ID is the pagename ID of the current page
$author = p_get_metadata($ID,'author');
$authorpage = ':user:'. str_replace(' ', '_',strtolower($author));
$uri = '/var/www/dokuwiki/data/pages' . str_replace(':','/',$authorpage) . '.txt';
print p_render('xhtml', p_get_instructions(io_readFile($uri)), $info);
?>
'/var/www/dokuwiki/data/pages' is not really canonic, do you know how to find this variable ?