<style type="text/css">

#dhtmltooltip{
position: absolute;
width: 150px;
border: 2px solid black;
padding: 2px;
background-color: lightyellow;
visibility: hidden;
z-index: 100;
/*Remove below line to remove shadow. Below line should always appear last within this CSS*/
filter: progid:DXImageTransform.Microsoft.Shadow(color=gray,direction=135);
}

</style>

<div id="dhtmltooltip"></div>

<script type="text/javascript">

/***********************************************
* Cool DHTML tooltip script- © Dynamic Drive DHTML code library (www.dynamicdrive.com)
* This notice MUST stay intact for legal use
* Visit Dynamic Drive at http://www.dynamicdrive.com/ for full source code
***********************************************/

var offsetxpoint=-60 //Customize x offset of tooltip
var offsetypoint=20 //Customize y offset of tooltip
var ie=document.all
var ns6=document.getElementById && !document.all
var enabletip=false
if (ie||ns6)
var tipobj=document.all? document.all["dhtmltooltip"] : document.getElementById? document.getElementById("dhtmltooltip") : ""

function ietruebody(){
return (document.compatMode && document.compatMode!="BackCompat")? document.documentElement : document.body
}

function ddrivetip(thetext, thecolor, thewidth){
if (ns6||ie){
if (typeof thewidth!="undefined") tipobj.style.width=thewidth+"px"
if (typeof thecolor!="undefined" && thecolor!="") tipobj.style.backgroundColor=thecolor
tipobj.innerHTML=thetext
enabletip=true
return false
}
}

function positiontip(e){
if (enabletip){
var curX=(ns6)?e.pageX : event.x+ietruebody().scrollLeft;
var curY=(ns6)?e.pageY : event.y+ietruebody().scrollTop;
//Find out how close the mouse is to the corner of the window
var rightedge=ie&&!window.opera? ietruebody().clientWidth-event.clientX-offsetxpoint : window.innerWidth-e.clientX-offsetxpoint-20
var bottomedge=ie&&!window.opera? ietruebody().clientHeight-event.clientY-offsetypoint : window.innerHeight-e.clientY-offsetypoint-20

var leftedge=(offsetxpoint<0)? offsetxpoint*(-1) : -1000

//if the horizontal distance isn't enough to accomodate the width of the context menu
if (rightedge<tipobj.offsetWidth)
//move the horizontal position of the menu to the left by it's width
tipobj.style.left=ie? ietruebody().scrollLeft+event.clientX-tipobj.offsetWidth+"px" : window.pageXOffset+e.clientX-tipobj.offsetWidth+"px"
else if (curX<leftedge)
tipobj.style.left="5px"
else
//position the horizontal position of the menu where the mouse is positioned
tipobj.style.left=curX+offsetxpoint+"px"

//same concept with the vertical position
if (bottomedge<tipobj.offsetHeight)
tipobj.style.top=ie? ietruebody().scrollTop+event.clientY-tipobj.offsetHeight-offsetypoint+"px" : window.pageYOffset+e.clientY-tipobj.offsetHeight-offsetypoint+"px"
else
tipobj.style.top=curY+offsetypoint+"px"
tipobj.style.visibility="visible"
}
}

function hideddrivetip(){
if (ns6||ie){
enabletip=false
tipobj.style.visibility="hidden"
tipobj.style.left="-1000px"
tipobj.style.backgroundColor=''
tipobj.style.width=''
}
}

document.onmousemove=positiontip

</script>

onMouseover="ddrivetip('JavaScriptKit.com JavaScript tutorials','yellow', 300)";
onMouseout="hideddrivetip()"

Nice Tutorial and nice Scripts
Thanks all
But i tell u dont use popup because Some Kind of firewalls Block Popup pages like ZoneAlarm and
Some browsers Dont support Popup
Like : IE6 + SP2 _full

Yes, a div layer popup, would look the best... (javascript alerts really get annoying, epsecially if the user is scrolling down, and happens to roll over your link.  Then they have to move thier mouse all the way to the "ok" button to contine... like i said:  very annoying