sitelink1 http://www.solucior.com/18-Javascript_opacity.html 
sitelink2 http://blogs.msdn.com/b/ie/archive/2008/...sions.aspx 
sitelink3  
sitelink4  
extra_vars5  
extra_vars6  

1. 속성별 지원 브라우저

opacity // modern browser
-moz-opacity // older versions based on firefox
-khtml-opacity // older versions based on Konkeror and Safari
filter: alpha(opacity) // Internet Explorer before 8.0
-ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity)" // Internet Explorer 8.0+


2. 샘플 코드

<script type="text/javascript">
   function
opacity(elm, value) {
       
elm.style.opacity = (value / 10);
       
elm.style.MozOpacity = (value / 10);
       
elm.style.KhtmlOpacity = (value / 10);
       
elm.style.filter = "alpha(opacity=" + (value * 10) + ")";
       
elm.style.MsFilter = " 'progid:DXImageTransform.Microsoft.Alpha(opacity=" + (value * 10) + ")' ";
   }
</script>
<img src="picture1.gif" alt=" " style="width: 400px; height: 50px" onmouseover="opacity(this, 5)" onmouseout="opacity(this, 10)" />