test

HTML

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js"></script>
look at browser console

JavaScript

// check the jquery version every tick
var timer = setInterval(function(){
    if(typeof $ != "undefined") {
        if($.fn.jquery != "1.5.2") {
            console.log("THIS SHOULD NOT HAPPEN: "+$.fn.jquery);
            clearInterval(timer);
        }
    }
},10);

// log output
console.log("running");

// attach new jquery library
var newjQuery, readyOnce = true;
function ready(type) {
    console.log("ready trigger "+type+": "+$.fn.jquery);
    if(readyOnce) {
        if($.fn.jquery == "1.8.3") newjQuery = window.jQuery.noConflict(true);
        readyOnce = false;
    }
}

var script = document.createElement("script");
script.setAttribute("type", "text/javascript");
script.setAttribute("src", "http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js");
  console.log("listening for readystatechange");
  script.onreadystatechange = function() {
    if (script.readyState === "complete" || script.readyState === "loaded") {
      ready("state");
    }
  };
  console.log("listening for onload");
  script.onload = function() {
    ready("load");
  };

(document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script);
console.log("after attach: "+$.fn.jquery);