For CSS background-images

.yourselector {
width:200px;
height:100px;
background: url(/folder/yourimage.png) no-repeat;
_background:none;
_filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='/folder/yourimage.png',sizingMethod='crop');
}

For inline HTML images

img, .png {
       position: relative;
       behavior: expression((this.runtimeStyle.behavior="none")&&(this.pngSet?this.pngSet=true:(this.nodeName == "IMG" && this.src.toLowerCase().indexOf('.png')>-1?(this.runtimeStyle.backgroundImage = "none",
       this.runtimeStyle.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='" + this.src + "', sizingMethod='image')",
       this.src = "images/transparent.gif"):(this.origBg = this.origBg? this.origBg :this.currentStyle.backgroundImage.toString().replace('url("','').replace('")',''),
       this.runtimeStyle.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='" + this.origBg + "', sizingMethod='crop')",
       this.runtimeStyle.backgroundImage = "none")),this.pngSet=true));
}