function get_object(id) {
   var object = null;
   if( document.layers ) {   
	object = document.layers[id];
   } else if( document.all ) {
	object = document.all[id];
   } else if( document.getElementById ) {
	object = document.getElementById(id);
   }
   return object;
}

function bgposition(divID,level) {
	//alert(pxw + 'px ' + pxh + 'px');
	var divOffset = -1 * level * document.getElementById(divID).offsetHeight;
	get_object(divID).style.backgroundPosition = '0px ' + divOffset + 'px';
}

function bgreset(divID) {
	get_object(divID).style.backgroundPosition = 'top';
}