It looks like each property overlay box is stored on the html page like this:
<map id="poiImageMap-1" name="poiImageMap-1">
<area id="poi_93955716" class="type_10002 group" shape="rect" coords="630,168,646,184" title="FINN-eiendom-solgt" href="">
<area id="poi_93955715" class="type_10002 group" shape="rect" coords="578,50,594,66" title="FINN-eiendom-solgt" href="">
[...]
</map>
And once you click on one of the overlays, the box pops up that contains the information you want, and is displayed somewhere in the html code (example too long to post here).
You could write a parser to scrape through this page, clicking each overlay and then recording the data that appears in the popup box.