With this code you can retrieve if jquery is set in your script, if jquery is not set then the script load it dinamically and set it.
(function () { var jQuery; if (window.jQuery === undefined || window.jQuery.fn.jquery !== '1.4.2') { var script_tag = document.createElement('script'); script_tag.setAttribute("type", "text/javascript"); script_tag.setAttribute("src", pathWidget + "/scripts/jquery-1.7.min.js"); if (script_tag.readyState) { script_tag.onreadystatechange = function () { // For old versions of IE if (this.readyState == 'complete' || this.readyState == 'loaded') { scriptLoadHandler(); } }; } else { script_tag.onload = scriptLoadHandler; } (document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag); } else { jQuery = window.jQuery; main(); } function scriptLoadHandler() { jQuery = window.jQuery.noConflict(true); main(); } function main() { jQuery(document).ready(function ($) { }); } })();