session variables
I did it like this...
On your confirm page, set a session variable for each field in your checkout form.
eg firstname
<?php
if (!session_id()) session_start();
if($_SERVER["REQUEST_METHOD"] == "POST") {
$_SESSION["eCartCheckoutForm_firstname"] = "".((isset($_POST["firstname"]))?$_POST["firstname"]:"") ."";
}
?>
On your checkout page your firstname field should look like this...
<input type="text" name="firstname" id="firstname" value="<?php if (isset($_SESSION['eCartCheckoutForm_firstname'])){ echo $_SESSION['eCartCheckoutForm_firstname'];} ?>"/></td>
repeat for the remaining fields.