Q: What do I do if I want to launch a group of screensavers randomly, like the way I randomize wallpaper?
A: For XP, I used to recommend ScreenSaver Druid, but that one has a relatively odd interface. I tried Random ScreenSaver Starter, but it crashes on Vista. So I recommend the free ScreenSaver Commander. It works perfectly in Vista, and you can activate / deactivate individual screensavers, order them in a list or go at random, with no problems, at all. Its only problem is that it doesn't read the Screensaver names properly. For example, the Screentime "Sunset 23" is read as "ScreenTime Screensaver Engine". However, it also shows the filename, which will tell you which screensaver that was.

Q: How about a wallpaper randomizer as well?
A: I use John's Background Switcher. It can download RSS feeds (example: flicker top 100), filter those feeds (Flickr Top 250 that had to do with cars), as well as play pictures from a directory, and more. It can even add a calendar and other features. And it is absolutely free. Obviously, to download you need to be online.
A second option is Wallpaper from MSN, which not only gives you some of the best licensed wallpaper from major movies (some examples are Slumdog Millionaire, Yes Man, Notorious, Hancock), but also major games (Prince of Persia, PGR4, LEGO Batman) and your regular landscapes, closeups, nature, and so on. What's more, you can edit those by adding additional characters and dialog bubbles/boxes. It will also do "slideshow" if you want it to.