json_decode function is not part of PHP 5.1, so I cannot use it. Is there any other function for this version?
You can use jsonwrapper library...
jsonwrapper implements the json_encode function if it is missing, and leaves it alone if it is already present. So it is nicely future-compatible.
Download here: jsonwrapper
To use just do:
require ("jsonwrapper.php");
$data = array('idx1' => 'foo', 'idx2' => 'bar');
echo json_encode($data);
echo json_decode($data);