Load jQuery only if it hasn't already been included somewhere on the page.

loadJQuery.js

/* Load jQuery only if needed */
(function(){
    var scriptAdded = false, js;
    
    function initJQuery() {
        if(typeof(jQuery) === 'undefined'){
            if(!scriptAdded){
                js = document.createElement('script');
                js.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js';
                var first = document.getElementsByTagName('script')[0];
                first.parentNode.insertBefore(js, first);
                scriptAdded = true;
            }
            setTimeout(initJQuery, 50);
        } else {
            // Do what you need to do with jQuery here.
        }
    }
    initJQuery();
})();