in order to receive a list of all element that contains the name, you can write:
$name = $_POST['name'];
$result = mysql_query("SELECT * FROM `agents_infos` WHERE ( agent_name LIKE '%".$name."%' )");
to avoid code injection i advice to use
$name = mysql_real_escape_string( $_POST['name'] );
instead of
$name = $_POST['name'];