//	this will iterate with each element with the class 'ie-fix-opacity' and add an IE filter,
		//	replacing the background-image for the filter of that image
		var version = parseFloat(navigator.appVersion.split('MSIE')[1]);
		if ((version >= 5.5) && (version < 7) && (document.body.filters)) {
			document.getElementsByClassName('ie-fix-opacity').each(function(poElement){
				// if IE5.5+ on win32, then display PNGs with AlphaImageLoader
				var cBGImg = poElement.currentStyle.backgroundImage;
				var cImage = cBGImg.substring(cBGImg.indexOf('"') + 1, cBGImg.lastIndexOf('"'));
						
				poElement.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='" + cImage + "', sizingMethod='scale')";
				poElement.style.backgroundImage = "none";
			});
		}

IE 5.5 & IE6  PNG Transparency Fix (Prototype required)

ie

JavaScript