Creo que lo que quieres es un mouseoer image popup estube buskando y encontré esto espero que te sea útil
<script type="text/javascript">
/***********************************************
* Image w/ description tooltip- By Dynamic Web Coding (
www.dyn-web.com)
* Copyright 2002-2007 by Sharon Paine
* Visit Dynamic Drive at
http://www.dynamicdrive.com/ for full source code
***********************************************/
/* IMPORTANT: Put script after tooltip div or
put tooltip div just before </BODY>. */
var dom = (document.getElementById) ? true : false;
var ns5 = (!document.all && dom || window.opera) ? true: false;
var ie5 = ((navigator.userAgent.indexOf("MSIE")>-1) && dom) ? true : false;
var ie4 = (document.all && !dom) ? true : false;
var nodyn = (!ns5 && !ie4 && !ie5 && !dom) ? true : false;
var origWidth, origHeight;
// avoid error of passing event object in older browsers
if (nodyn) { event = "nope" }
/////////////////////// CUSTOMIZE HERE ////////////////////
// settings for tooltip
// Do you want tip to move when mouse moves over link?
var tipFollowMouse= true;
// Be sure to set tipWidth wide enough for widest image
var tipWidth= 160;
var offX= 20; // how far from mouse to show tip
var offY= 12;
var tipFontFamily= "Verdana, arial, helvetica, sans-serif";
var tipFontSize= "8pt";
// set default text color and background color for tooltip here
// individual tooltips can have their own (set in messages arrays)
// but don't have to
var tipFontColor= "#000000";
var tipBgColor= "#DDECFF";
var tipBorderColor= "#000080";
var tipBorderWidth= 3;
var tipBorderStyle= "ridge";
var tipPadding= 4;
// tooltip content goes here (image, description, optional bgColor, optional textcolor)
var messages = new Array();
// multi-dimensional arrays containing:
// image and text for tooltip
// optional: bgColor and color to be sent to tooltip
messages[0] = new Array('red_balloon.gif','Here is a red balloon on a white background',"#FFFFFF");
messages[1] = new Array('duck2.gif','Here is a duck on a light blue background.',"#DDECFF");
messages[2] = new Array('test.gif','Test description','black','white');
//////////////////// END OF CUSTOMIZATION AREA ///////////////////
// preload images that are to appear in tooltip
// from arrays above
if (document.images) {
var theImgs = new Array();
for (var i=0; i<messages.length; i++) {
theImgs[i] = new Image();
theImgs[i].src = messages[i][0];
}
}
// to layout image and text, 2-row table, image centered in top cell
// these go in var tip in doTooltip function
// startStr goes before image, midStr goes between image and text
var startStr = '<table width="' + tipWidth + '"><tr><td align="center" width="100%"><img src="';
var midStr = '" border="0"></td></tr><tr><td valign="top">';
var endStr = '</td></tr></table>';
////////////////////////////////////////////////////////////
// initTip - initialization for tooltip.
// Global variables for tooltip.
// Set styles
// Set up mousemove capture if tipFollowMouse set true.
////////////////////////////////////////////////////////////
var tooltip, tipcss;
function initTip() {
if (nodyn) return;
tooltip = (ie4)? document.all['tipDiv']: (ie5||ns5)? document.getElementById('tipDiv'): null;
tipcss = tooltip.style;
if (ie4||ie5||ns5) { // ns4 would lose all this on rewrites
tipcss.width = tipWidth+"px";
tipcss.fontFamily = tipFontFamily;
tipcss.fontSize = tipFontSize;
tipcss.color = tipFontColor;
tipcss.backgroundColor = tipBgColor;
tipcss.borderColor = tipBorderColor;
tipcss.borderWidth = tipBorderWidth+"px";
tipcss.padding = tipPadding+"px";
tipcss.borderStyle = tipBorderStyle;
}
if (tooltip&&tipFollowMouse) {
document.onmousemove = trackMouse;
}
}
window.onload = initTip;
/////////////////////////////////////////////////
// doTooltip function
// Assembles content for tooltip and writes
// it to tipDiv
/////////////////////////////////////////////////
var t1,t2; // for setTimeouts
var tipOn = false; // check if over tooltip link
function doTooltip(evt,num) {
if (!tooltip) return;
if (t1) clearTimeout(t1); if (t2) clearTimeout(t2);
tipOn = true;
// set colors if included in messages array
if (messages[num][2]) var curBgColor = messages[num][2];
else curBgColor = tipBgColor;
if (messages[num][3]) var curFontColor = messages[num][3];
else curFontColor = tipFontColor;
if (ie4||ie5||ns5) {
var tip = startStr + messages[num][0] + midStr + '<span style="font-family:' + tipFontFamily + '; font-size:' + tipFontSize + '; color:' + curFontColor + ';">' + messages[num][1] + '</span>' + endStr;
tipcss.backgroundColor = curBgColor;
tooltip.innerHTML = tip;
}
if (!tipFollowMouse) positionTip(evt);
else t1=setTimeout("tipcss.visibility='visible'",100);
}
var mouseX, mouseY;
function trackMouse(evt) {
standardbody=(document.compatMode=="CSS1Compat")? document.documentElement : document.body //create reference to common "body" across doctypes
mouseX = (ns5)? evt.pageX: window.event.clientX + standardbody.scrollLeft;
mouseY = (ns5)? evt.pageY: window.event.clientY + standardbody.scrollTop;
if (tipOn) positionTip(evt);
}
/////////////////////////////////////////////////////////////
// positionTip function
// If tipFollowMouse set false, so trackMouse function
// not being used, get position of mouseover event.
// Calculations use mouseover event position,
// offset amounts and tooltip width to position
// tooltip within window.
/////////////////////////////////////////////////////////////
function positionTip(evt) {
if (!tipFollowMouse) {
standardbody=(document.compatMode=="CSS1Compat")? document.documentElement : document.body
mouseX = (ns5)? evt.pageX: window.event.clientX + standardbody.scrollLeft;
mouseY = (ns5)? evt.pageY: window.event.clientY + standardbody.scrollTop;
}
// tooltip width and height
var tpWd = (ie4||ie5)? tooltip.clientWidth: tooltip.offsetWidth;
var tpHt = (ie4||ie5)? tooltip.clientHeight: tooltip.offsetHeight;
// document area in view (subtract scrollbar width for ns)
var winWd = (ns5)? window.innerWidth-20+window.pageXOffset: standardbody.clientWidth+standardbody.scrollLeft;
var winHt = (ns5)? window.innerHeight-20+window.pageYOffset: standardbody.clientHeight+standardbody.scrollTop;
// check mouse position against tip and window dimensions
// and position the tooltip
if ((mouseX+offX+tpWd)>winWd)
tipcss.left = mouseX-(tpWd+offX)+"px";
else tipcss.left = mouseX+offX+"px";
if ((mouseY+offY+tpHt)>winHt)
tipcss.top = winHt-(tpHt+offY)+"px";
else tipcss.top = mouseY+offY+"px";
if (!tipFollowMouse) t1=setTimeout("tipcss.visibility='visible'",100);
}
function hideTip() {
if (!tooltip) return;
t2=setTimeout("tipcss.visibility='hidden'",100);
tipOn = false;
}
document.write('<div id="tipDiv" style="position:absolute; visibility:hidden; z-index:100"></div>')
</script>
leelo bien para que lo entiendsas mejor ademas te dejo la web aka
http://www.dynamicdrive.com/dynamici...agetooltip.htm