Google Searchbox Not Validating as HTML5

Hi!  I have added the Google searchbox to my HTML5 site. When I go to the
W3C validator I get an error: 'element gcse:search not allowed as child of
element div in this context'. I was instructed by Google to put the script
in a div, and cannot get the searchbox to work without it. My code is below.
Many thanks!  Julian

<div id="searchbox">    
    <script>
       (function() {    
            var cx = '014531685129972083622:vk5kxnojpx0';    
            var gcse = document.createElement('script');    
            gcse.type = 'text/javascript';    
            gcse.async = true;    
            gcse.src = (document.location.protocol == 'https:' ? 'https:' :
'http:') + '//www.google.com/cse/cse.js?cx=' + cx;

            var s = document.getElementsByTagName('script')[0];

            s.parentNode.insertBefore(gcse, s);

        })();

    </script>    
    <gcse:search> </gcse:search>    
 </div>