Полезный плагин. Очень легок в установке и настройке.

javascript:

var qTipTag = "a,label,input"; //Which tag do you want to qTip-ize? Keep it lowercase!//
var qTipX = 0; //This is qTip's X offset//
var qTipY = 15; //This is qTip's Y offset//

//There's No need to edit anything below this line//
tooltip = {
name : "qTip",
offsetX : qTipX,
offsetY : qTipY,
tip : null
}

tooltip.init = function () {
var tipNameSpaceURI = "http://www.w3.org/1999/xhtml";
if(!tipContainerID){ var tipContainerID = "qTip";}
var tipContainer = document.getElementById(tipContainerID);

if(!tipContainer) {
tipContainer = document.createElementNS ? document.createElementNS(tipNameSpaceURI, "div") : document.createElement("div");
tipContainer.setAttribute("id", tipContainerID);
document.getElementsByTagName("body").item(0).appendChild(tipContainer);
}

if (!document.getElementById) return;
this.tip = document.getElementById (this.name);
if (this.tip) document.onmousemove = function (evt) {tooltip.move (evt)};

var a, sTitle, elements;

var elementList = qTipTag.split(",");
for(var j = 0; j < elementList.length; j++)
{
elements = document.getElementsByTagName(elementList[j]);
if(elements)
{
for (var i = 0; i < elements.length; i ++)
{
a = elements[i];
sTitle = a.getAttribute("title");
if(sTitle)
{
a.setAttribute("tiptitle", sTitle);
a.removeAttribute("title");
a.removeAttribute("alt");
a.onmouseover = function() {tooltip.show(this.getAttribute('tiptitle'))};
a.onmouseout = function() {tooltip.hide()};
}
}
}
}
}

tooltip.move = function (evt) {
var x=0, y=0;
if (document.all) {//IE
x = (document.documentElement && document.documentElement.scrollLeft) ? document.documentElement.scrollLeft : document.body.scrollLeft;
y = (document.documentElement && document.documentElement.scrollTop) ? document.documentElement.scrollTop : document.body.scrollTop;
x += window.event.clientX;
y += window.event.clientY;

} else {//Good Browsers
x = evt.pageX;
y = evt.pageY;
}
this.tip.style.left = (x + this.offsetX) + "px";
this.tip.style.top = (y + this.offsetY) + "px";
}

tooltip.show = function (text) {
if (!this.tip) return;
this.tip.innerHTML = text;
this.tip.style.display = "block";
}

tooltip.hide = function () {
if (!this.tip) return;
this.tip.innerHTML = "";
this.tip.style.display = "none";
}

window.onload = function () {
tooltip.init ();
}

CSS: 

div#qTip {
padding: 3px;
border: 1px solid #666;
border-right-width: 2px;
border-bottom-width: 2px;
display: none;
background: #999;
color: #FFF;
font: bold 9px Verdana, Arial, sans-serif;
text-align: left;
position: absolute;
z-index: 1000;
}