var pos=100;
var muv

function startit(){

muv=window.setTimeout("Scroll();",30);
}

function stopit(){

window.clearTimeout(muv);
}

function Scroll() {
  if (!document.getElementById) return;  
  obj=document.getElementById("linktar");  
  pos -=1;  
  if (pos < 0-obj.offsetHeight) pos = obj.offsetHeight; 
  obj.style.top=pos;
   muv=window.setTimeout("Scroll();",30);}