I generally don't like regurgitating other people's "content," so to speak. That said, I'm happily re-reporting on more updates and add-ons to a program you may have seen before. "John's Background Switcher" is a free Windows-only program that does only as named; its not "John's Expensive Program That May Or May Not Work" or "John's Bloated Spyware Memory Hog."
It uses about as much memory on my laptop as Thunderbird does (although I have 2GB of RAM), and really does work, for free. Beyond even the novelty of a program changing your background on your terms, it can not only use local pictures and local folders (this is how you can use the really nifty choices - more later), but suck in photo albums, or tagged photos from flickr (top 10 cute pictures of Nadja or Romana), picasa, and yahoo among others.
Besides just displaying an image on the desktop, and switching it
for you, when you select a local folder the nifty features I mentioned appear: the ability to create a "snapshot scrapbook," a "four-picture montage," and "thumbnail mosaic."
It can also stretch, center, scale, and over-scale pictures (just select them all and right-click) for your local resolution.
Best of all, its fairly intuitive (did I mention FREE?), and clean-looking, and lightweight.
It makes me want to up the delay of the cool screensaver I was all excited about a few weeks ago. Confession: I put it on all the computers at work. :/