var currentpos,timer; 
function scrollit() 
{ 
timer=setInterval("scrollwindow()",10);
} 
function stopit(){
clearInterval(timer); 
}
function scrollwindow() 
{ 
currentpos=document.body.scrollTop; 
window.scroll(0,++currentpos); 
if (currentpos != document.body.scrollTop) 
stopit();
} 
document.onmousedown=stopit
document.ondblclick=scrollit