Touché, what you'd like seems to me should be easy to find. Apparently not so. Probably because it's better to shut down PPC and save battery. But if PPC is sitting idle in a charging cradle, for example, an auto slideshow after a couple minutes makes good sense. I've not seen anything exactly like that, but some time ago I did see something sort of close. It's called SereneScene, costs $9.95, and plays an animated aquarium screensaver with a few user definable variables. Let's hope somebody finds something better. In the meanwhile, here are a couple links.
Here's where I learned about it (scroll down abeery's post):
http://tinyurl.com/9k7jeb
Here's where it can be purchased:
http://www.serenescreen.com/product/ma-ppc/
Warning - The guy programmer wrote this app admits it uses lots of resources, like RAM and battery, so it's really meant only for use while idle and on external power.