Highlight a section of an image in JavaScript

Instead of using image maps, you could try this CSS method:

Use a transparent <div> on top of each "image-map" part (link), and then use the CSS :hover pseudo-class to handle the highlighting.

CSS:

#image { 
    position: relative; 
    width: 400px;
    height: 100px; 
    background-image: url(image_map.png); 
}

#map-part { 
    position: absolute; 
    top: 10px; 
    left: 10px; 
    width: 50px; 
    height: 50px; 
    background-color: transparent;  
}   

#map-part:hover { 
    background-color: yellow;           /* Yellow Highlight On Hover */
    opacity: 0.2;
    filter: alpha(opacity=20);      
}

HTML:

<div id="image">
    <a id="map-part" href="http://www.example.com/"></a>
</div>

Note that this will only work for rectangular links.

Take a look at jQuery MapHilight.
I'm not sure it does exactly what you need, but you can achieve that with minor tweaking.