When you are using jQuery with other Javascript libraries such as Prototype. There will be conflict on the $() function. There are 3 ways to bypass the conflict.
1. Only use jQuery() for the jQuery calls and revert the $() to Prototype
jQuery.noConflict();
// Use jQuery via jQuery(...)
jQuery(document).ready(function(){
jQuery("div").hide();
});
// Use Prototype with $(...), etc.
$('someid').hide();