function zxcWWHS(){
 if (document.all){
  zxcCur='hand';
  zxcWH=document.documentElement.clientHeight;
  zxcWW=document.documentElement.clientWidth;
  zxcWS=document.documentElement.scrollTop; //ie trans & strict
  if (zxcWH==0){
   zxcWS=document.body.scrollTop; //ie trans & strict
   zxcWH=document.body.clientHeight;
   zxcWW=document.body.clientWidth;
  }
 }
 else if (document.getElementById){
  zxcCur='pointer';
  zxcWH=window.innerHeight-15;
  zxcWW=window.innerWidth-15;
  zxcWS=window.pageYOffset;
 }
 zxcWC=Math.round(zxcWW/2);
 return [zxcWW,zxcWH,zxcWS];
}

function zxcScrollTop(){
 zxcS=0;
 if (!document.all){ zxcST=window.pageYOffset; }
 else if (!document.body.scrollTop){ zxcST=document.documentElement.scrollTop; }
 else { zxcST=document.body.scrollTop; }
 gtts.top=(zxcST+zxcWWHS()[1]-gtt.offsetHeight)+'px';
 return zxcST;
}

window.onscroll=zxcScrollTop;

function gttPosition(){
 gtt=document.getElementById('GotoTop');
 gtts=gtt.style;
 gtts.left=(zxcWWHS()[0]-gtt.offsetWidth-20)+'px';
//or the distance left you require
 zxcScrollTop();
}

function Top(){
  window.scroll(0,0);
}