I'd been meaning to put a page up about this for _years_! I finally got around to it tonight. Give it a look! Sorry for the rather lengthy read. The pictures are towards the bottom.
One thing I did a little differently with this hack was to implement "Program Linking" between the picture frame and a 2nd Mac on the network via AppleScript applications. This allows me to do all sorts of fun things on the picture frame without requiring the use of a keyboard or mouse. If I ever go one step farther and install VNC, it'll be a pretty slick setup.