So, there's no way that this works:
window.onload = function(){
<script language="JavaScript" src="http://jact.atdmt.com/jaction/JavaScriptTest"></script>
};
You can't freely drop HTML into the middle of javascript.
If you have jQuery, you can just use:
$.getScript("http://jact.atdmt.com/jaction/JavaScriptTest")
whenever you want. If you want to make sure the document has finished loading, you can do this:
$(document).ready(function() {
$.getScript("http://jact.atdmt.com/jaction/JavaScriptTest");
});
In plain javascript, you can load a script dynamically at any time you want to like this:
var tag = document.createElement("script");
tag.src = "http://jact.atdmt.com/jaction/JavaScriptTest";
document.getElementsByTagName("head")[0].appendChild(tag);