First of all, I would never use adsense on a personal site, but than again this is perhaps no personal site :).
It's more difficult because you would have to include the google code inside collections.php, but it's possible I think. Something like this (look near the bottom of the code):
// generate XHTML with thumbnail and link to picture view. print '<img class="photos" src="'.plogger_get_collection_thumb().'" title="'.$desc.'" alt="'.$desc.'" />';
<li> should get a display:block and float:left. Since you will have only two <li> in that place it could work this way. I thinks this wil ask for some trial and error :) since I don't know what kind of code Google uses.