Here is an example to do it
<a href="#" class="tip">Link<span>This is the CSS tooltip showing up when you mouse over the link</span></a>
CSS part:
A.tip {
BORDER-BOTTOM: 1px dashed; TEXT-DECORATION: none
}
A.tip:hover {
CURSOR: help; POSITION: relative
}
A.tip SPAN { DISPLAY: none
}
A.tip:hover SPAN {
BORDER-RIGHT: #c0c0c0 1px dotted; PADDING-RIGHT: 20px; BORDER-TOP: #c0c0c0 1px dotted; DISPLAY: block; PADDING-LEFT: 5px; Z-INDEX: 100; BACKGROUND: url(../images/status-info.png) #f0f0f0 no-repeat 100% 5%; LEFT: 0px; PADDING-BOTTOM: 5px; MARGIN: 10px; BORDER-LEFT: #c0c0c0 1px dotted; WIDTH: 250px; PADDING-TOP: 5px; BORDER-BOTTOM: #c0c0c0 1px dotted; POSITION: absolute; TOP: 10px; TEXT-DECORATION: none
}