var x = 50,y = 60  
var xin = true, yin = true  
var step = 1    
var delay = 20  
var obj=document.getElementById("ad")    
function floatAD() {   
  var L=T=0  
  var R= document.body.clientWidth-obj.offsetWidth   
  var B = document.body.clientHeight-obj.offsetHeight   
  obj.style.left = x + document.body.scrollLeft   
  obj.style.top = y + document.body.scrollTop   
  x = x + step*(xin?1:-1)    
  if (x < L) { xin = true; x = L}    
  if (x > R){ xin = false; x = R}    
  y = y + step*(yin?1:-1)    
  if (y < T) { yin = true; y = T }    
  if (y > B) { yin = false; y = B }    
}   
var itl= setInterval("floatAD()", delay)    
obj.onmouseover=function(){clearInterval(itl)}    
obj.onmouseout=function(){itl=setInterval("floatAD()", delay)}
function hide(){obj.style.visibility="hidden";}