var  xPos  =  20; 
var  yPos  =  document.body.clientHeight; 
var  step  =  1; 
var  delay  =  30;   
var  height  =  0; 
var  Hoffset  =  0; 
var  Woffset  =  0; 
var  yon  =  0; 
var  xon  =  0; 
var  pause  =  true; 
var  interval; 
img.style.top  =  yPos; 
function  changePos()  { 
width  =  document.body.clientWidth; 
height  =  document.body.clientHeight; 
Hoffset  =  img.offsetHeight; 
Woffset  =  img.offsetWidth; 
img.style.left  =  xPos  +  document.body.scrollLeft; 
img.style.top  =  yPos  +  document.body.scrollTop; 
if  (yon)  { 
yPos  =  yPos  +  step; 
} 
else  { 
yPos  =  yPos  -  step; 
} 
if  (yPos  <  0)  { 
yon  =  1; 
yPos  =  0; 
} 
if  (yPos  >=  (height  -  Hoffset))  { 
yon  =  0; 
yPos  =  (height  -  Hoffset); 
} 
if  (xon)  { 
xPos  =  xPos  +  step; 
} 
else  { 
xPos  =  xPos  -  step; 
} 
if  (xPos  <  0)  { 
xon  =  1; 
xPos  =  0; 
} 
if  (xPos  >=  (width  -  Woffset))  { 
xon  =  0; 
xPos  =  (width  -  Woffset); 
      } 
} 
function  start()  { 
img.visibility  =  "visible"; 
interval  =  setInterval('changePos()',  delay); 
} 
start();