(function($){
	$.fn.rollOver = function(options) {

		var defaults = {
			over: "_on",
			element: "li",
			extension: "png",
			callbackOver: callbackOver,
			callbackOut: callbackOut
		};
				
		var options = $.extend(defaults, options);
		
		obj = $(this);
		
		$(obj).find(options.element).find("img").hover(
			function(){
				adr = $(this).attr("src").split(".")[0];
				$(this).attr("src",adr+options.over+"."+options.extension);
				options.callbackOver();
			},
			function(){
				adr = $(this).attr("src").split(options.over)[0];
				$(this).attr("src",adr+"."+options.extension);
				options.callbackOut();
			}
		);
		
		function callbackOver()
		{
			// Default action
		}
		
		function callbackOut()
		{
			// Default action
		}
		
		return this;
	};
})(jQuery);