var x = 50;
var y = 60;
var xin = true;
var yin = true;
var step = 1;
var delay = 10;
var obj=document.getElementById("ad"); 
function floatAD() {
var L=0;
var T=0;
var R= document.body.clientWidth-obj.offsetWidth;
var B = 520;
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);}

//