<style>
    a:hover {background:#ffffff; text-decoration:none;} /*BG color is a must for IE6*/
    a.tooltip span {display:none; padding:2px 3px; margin-left:8px; width:130px;}
    a.tooltip:hover span{display:inline; position:absolute; background:#ffffff; border:1px solid #cccccc; color:#6c6c6c;}
</style>

Usage:Tool-tipped link This will appear in a tool-tip

<a class="tooltip" href="#">Tool-tipped link<span> This will appear in a tool-tip</span></a>