Try this:
http://dynamicdrive.com/dynamicindex11/gradualfader.htm
Of course your probably thinking of this script that doesn't work anymore(outdated):
http://dynamicdrive.com/dynamicindex4/image5.htm
You could also try jquery:
http://jquery.com/
I've also just very quickly whipped up something:
<style type="text/css">
#menu {
width: %100;
height: 47px;
margin: 0;
paddding: 0;
}
#menu a:link, #menu a:visited {
font-family: arial, verdana;
font-size: 12px;
text-decoration: none;
display: block;
width: 104px;
height: 47px;
margin-bottom: 20px;
padding-top: 15px;
text-align: center;
color: #FFF;
background: url(bg.png) no-repeat;
}
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$('#menu a').each(function() {
$(this).css({
opacity: '0.4',
});
$(this).hover(function() {
$(this).animate({
opacity: '1',
});
},
function() {
$(this).animate({
opacity: '0.4',
});
});
});
});
</script>
<div id="menu"><a href="#">Home</a><a href="#">Contact</a></div>
And here's an example here (http://unlinkthis.net/examples/jquery/fadeIn%20links/).