哥们,你写错了.
应该是用pixelLeft 
// JavaScript Document self.onError=null;    
currentX = currentY = 0;    
whichIt = null;    
lastScrollX = 0; //最后离左边距离的负值 
lastScrollY =0;  //最后离顶部的高度的负值 
  
//----------------------start fun秒执行一次  
function heartBeat(id1,id2) {    
diffY = document.body.scrollTop; 
diffX = document.body.scrollLeft;  if(diffY != lastScrollY) {    
percent = .1 * (diffY - lastScrollY);    
if(percent > 0) percent = Math.ceil(percent);    
else percent = Math.floor(percent);    
id1.style.pixelTop += percent; 
id2.style.pixelTop += percent;  
lastScrollY = lastScrollY + percent;    
}     if(diffX != lastScrollX) {    
percent = .1 * (diffX - lastScrollX);    
if(percent > 0) percent = Math.ceil(percent);    
else percent = Math.floor(percent);    
id1.style.pixelLeft += percent; 
id2.style.pixelLeft += percent;      
lastScrollX = lastScrollX + percent;    
}    
}    scr=screen.width 
left_1=(scr>800)?10:145 
right_1=(scr>800)?1024:580 //左侧图片 
document.write(" <div id=f1 style='left: "+left_1+"px; top: 150px; POSITION: absolute;'> <img src=newyear/2009newyear_left.jpg width=120 height=500 border=0> </div>") //右侧图片 
document.write(" <div id=f2 style='left: "+right_1+"px; top: 150px; POSITION: absolute;'> <img src=newyear/2009newyear_right.jpg width=120 height=500 border=0> </div>") 
action = window.setInterval("heartBeat(f1,f2)",50);