var xPos = 200;
var yPos = 123; 
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;
img1.style.top = yPos;
function changePos() 
{
 width = document.documentElement.clientWidth;
 height = document.documentElement.clientHeight;
 Hoffset = img1.offsetHeight;
 Woffset = img1.offsetWidth;
 img1.style.left = xPos + document.documentElement.scrollLeft;
 img1.style.top = yPos + document.documentElement.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()
  {
   img1.visibility = "visible";
  interval = setInterval('changePos()', delay);
 }
 function pause_resume() 
 {
  if(pause) 
  {
   clearInterval(interval);
   pause = false;}
  else 
  {
   interval = setInterval('changePos()',delay);
   pause = true; 
   }
  }
 start();