CSS
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;}
HTML
Easy <a class="tooltip" href="#">Tooltip<span>This is the crazy little Easy Tooltip Text.</span></a>.