Thanks and Merry Christmas everyone. =)
I made few enhancements: http://gist.github.com/39905
The script will now parse through a directory hierarchy of photos, to include those set to match a query. The data is then formatted to fit the tag's URL style, so the links are absolute. Other formatting is done and then a virtually unlimited number of items can be added to the playlist.xml file.
My thumbnail slideshow at http:///markpreynolds.com includes about 1,200 photos. ( I wouldn't want to type that XML file by hand =)
I think a couple other fun enhancements would be:
1. Add a unique link tag for each photo to click through to the picture source.