var fadeFuncion  = function() {
        //now select the element you want to tween
        //then tack on .tween
        //finally declare the style property and value you want to tween to
	$('fade').tween('background-position', '0','-100px');
}

window.addEvent('domready', function() {
        //here we add an event to a button to initiate the tween on click
        //and we call our tween function
        $('.fade').addEvent('mouseenter', fadeFuncion);
});