copying fields in my form

gistfile1.txt

Taking your advice to do it in jQuery, this is what I NOW have above the form:

<script type="text/javascript">
	$(document).ready(function(){
		$("input#same").click(function(){
			if ($("input#same").is(':checked'))
			{
				// Checked, copy values
				$("input#first_name").val($("input#order_first_name").val());
				$("input#last_name").val($("input#order_last_name").val());
			}
			else
			{
				// Clear on uncheck
				$("input#first_name").val("");
				$("input#last_name").val("");
			}
		});
	});
</script>

And then the checkbox is:

<input type="checkbox" id="same">

But it's still not working for me. Stumped.