Warning*: session_start(), Cannot send session cache limiter ...
Put the declaration for the require_once as the first line of code on the page, then put the declaration for the grid object between the body tag of the html document.
e.g.
<?phprequire_once("../conf.php");
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>A Basic PHP Datagrid</title>
</head>
<body>
<?php
$dg = new C_DataGrid("SELECT * FROM orders", "orderNumber", "orders");
$dg -> display();
?>
</body>
</html>