When using jQuery with Sitecore you need to take additional steps so that the jQuery $ function doesn't interfere with the Prototype $ function that Sitecore uses for the Sitecore Ribbon.
Example from api.jquery.com
jQuery.noConflict();
(function($) {
$(function() {
// more code using $ as alias to jQuery
});
})(jQuery);
// other code using $ as an alias to the other library
See Also:
