I've never heard of an S-Video out for a PDA but they could exist. The user port on your average PDA might not have the bandwidth to drive a screen directly but there may be a gizmo that does the work of keeping a screen up to date for you and takes a PDA feed - I can see it being very costly though.
Another option would be a simple picture viewer - you can get quite nice ones designed for dumping the images from a digital still camera or camcorder and burning them to CD or DVD. The good ones can then play these back in a slideshow controlled by a little IR remote. The whole thing is about the size of a walkman.
Something like this:
Using the software others have identified above you could make a series of stills or a DVD menu (so you can control the speed it changes images at).
Alternativly, you could look at one of the smaller laptops. If you don't need to play high-end games and run crazy graphics packages you could get a very low-spec one.
Sony have a couple of very small laptops, including one about two or three times the size of a PDA (not so cheap though). Other manufacturers do little laptops too but I've not seen one quite as small as sony's:
