No, it is very simple. Take a look at the source. For each building you need to add this:
<area shape="poly"
coords="400,276,424,299,408,312,386,292"
onMouseOver="setVisible('temple2')"
onMouseOut="hideAll('temple2')"
href="http://www.eurobricks.com/forum/index.php?showtopic=63232"/>
and this
<div id='temple2' style="visibility:hidden;position:absolute;top:10px;">
<img src="http://www.brickshelf.com/gallery/volcanicpanik/Avalonia/TempleMars/dsc01209.jpg" width=400px>
</div>
The building id (temple2) should be the same all 3 places.
The hard part is the coords:
coords="400,276,424,299,408,312,386,292"
It is coordinates in the image (400,276), (424,299),(408,312),(386,292)
I think it could also be cool with at little text description for each moc, but I am too lazy :-D for now at least.
BTW: sorry for polluting the thread with code. If anybody want to update the map and need help, please just PM me.