CSS Image Swap

<div class="nav">

<a href="#">

<img src="logo.gif" width="187" height="136" alt="" />

</a>

</div>


And the CSS to go along with it:
div.nav {
height: 187px;
width: 136px;
margin:0;
padding:0;
background-image:url("logo-red.gif");
}

div.nav a, div.nav a:link, div.nav a:visited {
display:block;
}

div.nav img {
width:100%;height:100%;border:0;
}

div.nav a:hover img {
visibility:hidden;
}