I have quickly hacked together a Dekiscript template that will render a lightbox image gallery out of a Picasa XML export.
Short instructions and link to a demo gallery are on the page. Basically it displays the picasa thumbnails and links them to the subfolder with the large images in lightbox-style. Nothing fancy but it looks especially nice with a CMS skin ;-)
@SteveB: I borrowed your demo gallery images.. hope you don't mind...