I came accross this CSS tool tip here
Code:
<style>
a.info{
position:relative; /*this is the key*/
z-index:24; background-color:#ccc;
color:#000;
text-decoration:none
}
a.info:hover{z-index:25; background-color:#ff0}
a.info span{display: none}
a.info:hover span{ /*the span will display just on :hover state*/
display:block;
position:absolute;
top:2em; left:2em; width:15em;
border:1px solid #0cf;
background-color:#AAAA00; color:#000;
text-align: center
}
</style>
</head>
<body>
<a href="" class="info">test<span>Pure CSS Tooltips</span></a>
</body>