var navArrowSlider = function(navWrap, navElementsArray, activeID, arrowY, leftOffset) {
	var youAreHere = new Fx.Tween($(navWrap), { 
		duration: 1200,
		transition: Fx.Transitions.Elastic.easeOut  
	});

	$$(navElementsArray).each(function(item){  
		item.addEvent('mouseenter', function() { 
			var thisPos = item.getPosition(navWrap).x  + item.getSize().x - leftOffset; 
			youAreHere.cancel();
			youAreHere.start('background-position', thisPos + 'px ' + arrowY + 'px'); 
		});
	});
	
	var currentArrow = function() {
		youAreHere.cancel();
		var activePos = $(activeID).getPosition(navWrap).x  + $(activeID).getSize().x - leftOffset; 
		youAreHere.start('background-position', activePos + 'px ' + arrowY + 'px');      
	};
	
	var activePos = $(activeID).getPosition(navWrap).x  + $(activeID).getSize().x - leftOffset; 
	$(navWrap).setStyle('background-position', activePos + 'px ' + arrowY + 'px');       
	
	currentArrow(); 
	
	$(navWrap).addEvent('mouseleave', currentArrow);	
}; 
	
window.addEvent('domready', function() {
	navArrowSlider(
		'nav_wrap', 
		'#nav_wrap ul li', 
		'active_nav', 
		'0px', 
		'55' 
	); 	
});