function preloadImgs() {
	var d=document,a=arguments;
	if(!d.imgs)
		d.imgs=new Array();
	for(var i=0; i<a.length; i++) {
		d.imgs[i]=new Image;
		d.imgs[i].src=a[i]; 
	}
}

preloadImgs(
	'/images/nav_liactive_bg.png',
	'/images/nav_dd_liactive_bg.png',
	'/images/nav_li_last_active_bg.png'
)