GENERAL
The jQuery library, and virtually all of its plugins are constrained within the jQuery namespace. As a general rule, “global” objects are stored inside the jQuery namespace as well, so you shouldn’t get a clash between jQuery and any other library (like Prototype, MooTools, or YUI).
That said, there is one caveat: By default, jQuery uses “$” as a shortcut for “jQuery”
more info http://docs.jquery.com/Using_jQuery_with_Other_Libraries
<html>
<head>
<script src="prototype.js"></script>
<script src="jquery.js"></script>
<script>
jQuery.noConflict();
// Use jQuery via jQuery(...)
jQuery(document).ready(function(){
jQuery("div").hide();
});
// Use Prototype with $(...), etc.
$('someid').hide();
</script>
</head>
<body></body>
</html>