levo - 3:44 pm on Jul 29, 2011 (gmt 0)

<script type="text/javascript">
(function(){
jqhead=document.getElementsByTagName('head')[0];
var jqscript=document.createElement('script');
jqscript.type='text/javascript';
jqscript.async=true;
jqscript.src='yourscript.js';
jqhead.appendChild(jqscript);
})();
</script>

The trick is, you should put all jquery commands in that external script, after the jquery code. With async loading, if you put them after that code, or in other external js file, the browser might call them before jquery is loaded.