First use one of those dynamic tooltip things (for example):
(sorry apparently I'm not cool enough to post normal links)
walterzorn *dot* com /tooltip/tooltip_e *dot* htm
Then, when you do your image map, in the onmouseover event, set it to:
"return escape('Text with <img src=\'image.jpg\' width=\'60\'> image.')"
(Just like in the example from the above website).
Full Example:
<script language="JavaScript" type="text/javascript" src="wz_tooltip.js"></script>
...
<MAP NAME="TheMap">
<AREA SHAPE="RECT" COORDS="57, 78, 135, 138" HREF="normal_one.com" onMouseover="showtip(this,event,'This is a normal tooltip')"
onMouseout="hidetip()"><AREA SHAPE="RECT" COORDS="103, 10, 174, 75" HREF="wsabstract.com" onmouseover="return escape('Text with <img src=\'image.jpg\' width=\'60\'> image--this is a cooler tooltip!')"
onMouseout="hidetip()">
</MAP>
<img src="imagemap.gif" width="188" height="173" border="0" usemap="#TheMap">