请问如何实现png图片的背景在IE6下的透明效果？

代码示例：<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>alpha picture </title> 
<style type="text/css"> 
.leftAlpha{ 
width:250px; height:333px; 
float:left; 
background:#efefef; 
filter:alpha(opacity=50); /*IE*/ 
  -moz-opacity:0.5; /*MOZ , FF*/ 
  opacity:0.5; /*CSS3, FF1.5*/ 
} 
.rightAlpha{width:250px; height:333px; 
float:right; 
ackground:#efefef; 
filter:alpha(opacity=10); /*IE*/ 
  -moz-opacity:0.1; /*MOZ , FF*/ 
  opacity:0.1; /*CSS3, FF1.5*/ 
} 
#picture{ 
background:url(http://p.blog.csdn.net/images/p_blog_csdn_net/lfywy/400542/o_2008052714285782380.jpg) no-repeat; 
width:500px; height:333px; 
float:left; 
} 
</style> 
</head> <body> 
<div id="picture"> 
<div class="leftAlpha"> </div> 
<div class="rightAlpha"> </div> 
</div> 
</body> 
</html>