This is a very old thread. The Classifieds has an inc_ads.php file like Photopost has where you can set up featured ads.
You should be able to see the include needed but basically you create a php block in phpportals and echo the results. You should post in the mod forum on this type of thing.
Sorry but the very essense of my job work load dealing with support does not allow me free time to play with mods.