lastScrollY=0; 
function rollimg(){ 
var varY = document.body.scrollTop;
if (varY <= 0)
{
varY = document.documentElement.scrollTop;
}
percent=.1*(varY-lastScrollY);
if(percent >0 )
percent=Math.ceil(percent); 
else
percent=Math.floor(percent);
var top = parseInt(document.getElementById("scollAD").style.top);
document.getElementById("scollAD").style.top = (top += percent ) + "px";
lastScrollY += percent; 
document.getElementById("scollAD").style.left=(document.body.clientWidth-80)+"px";//(document.body.clientWidth/2+400)+"px";
}

window.setInterval("rollimg()",1);