IE6不支持PNG透明，支持GIF透明，但是GIF透明锯齿太多了，所以一般是用PNG，

然后引用JS让IE6支持。

<!--[if IE 6]>

<script>

function correctPNG()

{

for(var i=0; i<document.images.length; i++)

{

var img = document.images[i];

var imgName = img.src.toUpperCase();

if (imgName.substring(imgName.length-3, imgName.length) == "PNG")

{

var imgID = (img.id) ? "id='" + img.id + "' " : "";

var imgClass = (img.className) ? "class='" + img.className + "' " : "";

var imgTitle = (img.title) ? "title='" + img.title + "' " :

"title='" + img.alt + "' ";

if (img.align == "left") imgStyle = "float:left;" + imgStyle;

if (img.align == "right") imgStyle = "float:right;" + imgStyle;

if (img.parentElement.href) imgStyle = "cursor:hand;" + imgStyle;

var strNewHTML = "<span "+ imgID + imgClass + imgTitle + "style=

\"" + "width:" + img.width + "px; height:" + img.height + "px;

" + imgStyle + ";" + "filter:progid:DXImageTransform.Microsoft.

AlphaImageLoader" + "

(src='" + img.src + "', sizingMethod='scale');\"></span>";

i = i-1;

}

}

}

window.attachEvent("onload", correctPNG);

</script>

<![endif]-->

这段代码复制到</head>上面，就可以了。