Code to be placed in form html:

<?php
$product = JRequest::getVar('product', 0, 'get', 'string');    
$product1= str_replace ("_", " ", $product);
?>

...and

<input type="hidden" name="product_name" value="<?php echo $product1; ?>" />
<h1 class="cf_text">My Form - <?php echo $product1; ?></h1>