/* =Hoverbox Code= */
.hoverbox { cursor: default; list-style: none; padding: 0;}
.hoverbox a { cursor: default; }
.hoverbox a .preview { display: none; }
.hoverbox a:hover .preview { display: block; position: absolute; top: 0px; left: 0px; z-index: 1; }
.hoverbox img { background: transpanent; border-color: transpanent; border-style: solid; border-width: 0px; color: inherit; padding: 2px; vertical-align: top; }
.hoverbox li { background: white; color: inherit; display: inline; float: left; margin: 5px 10px 5px -25px; padding: 0px; position: relative; }
.hoverbox li.text { background: white; color: inherit; display: inline; float: left; margin: 0px 0px 0px 0px; padding: 0px; position: relative; }
.hoverbox .preview { border-color: transpanent; } 
/* ----------------- */

<ul class="hoverbox">
<li>
<a href="ссылка" target="_blank">
<img src="картинка 2" border="0" width="100"> 
<img class="preview" src="картинка 1" border="0" width="170"></a>
</li>
</ul>