var xPos = 20;//from webjx.com
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.style.visibility = "visible";                  
interval = setInterval('changePos()', delay);                    
}              
start();