I have Picasa integrated in with my Xlobby using Girder. I make it so that when I hit pictures, it opens up Picasa and use a Girder 3.3 GML file, I control Picasa so. You just set up Picasa to open up in Full Screen Mode and also use Send Focus to make sure it stays in the front. I have a GML file over at Girder that uses Picasa.
Is there a way to filter the pictures using the Picasa (or other) database? I have an ever increasing number of pictures (2 1/2 year old and one on the way) that are dumped into directories by date. Many are not great, but I can't bring myself to delete any. It would be nice to filter only the "Favorite" pictures for display in XLobby. Another neat trick would be an option to view the new ones and mark as favorite as well.
In Picasa, You can arrange pictures by year, date, folder location, and other features. The easiest way in your case is to possibly move the ones U like in one folder or area, and have another folder termed "older" or outdated photos.