Sadly the new Photo Browser photo layer doesn't appear to be available in the Google Maps API. However because the Photo Browser used in Google Maps is based on Flash you could grab the address of the Flash file for a particular Photo Browser and embed it in a map.
I've just had a quick look at the Panoramio API and created a slideshow that will load a photo into the Google Maps Photo Browser (without a map). To load a photograph into the browser just click on the next and back arrows thumbnail.
Although there is no map associated with this little app if you look at the source code you should be able to work out how you could add a Photo Browser to a Google Maps mashup.