ecco trovato quello che cercavo. se interessasse a qualcuno:

You can also store an array within the session array. Let's go back to our mypage.php file and edit it slightly to do this:

<?php
session_start();

// makes an array
$colors=array('red', 'yellow', 'blue');
// adds it to our session
$_SESSION['color']=$colors;
$_SESSION['size']='small';
$_SESSION['shape']='round';
print "Done";
?>

Now let's run this on mypage2.php to show our new information:

<?php
session_start();
Print_r ($_SESSION);
echo "

";

//echo a single entry from the array
echo $_SESSION['color'][2];
?>


naturalmente con le adeguate modifiche ma il concetto è questo.
grazie

fonte: http://php.about.com/od/advancedphp/...sessions_2.htm