I configured my Preferences so that the Slide Show screen saver showed the folder in which I store desktop backgrounds. Somehow it was screwed up (folder moved or something?) and every time I tried to access the screen saver preferences, the Preferences App crashed. Very annoying and very little you can do about it. It was not possible to change any setting, because as soon as the Screen Saver part of the preferences was shown it just quit.
But as a former Linux geek I'm used to things not working and things that need tweaking, so I created another user, logged in with that user and changed the screen saver settings. Then with Sherlock I searched for all files changed today. I found an interesting file in Library/Preferences/ByHost called com.apple.screensaver.*.plist. It's an XML file containing the screen saver settings.
Then I logged in again with my regular user, opened the Finder and opened the same file for my regular user. By double clicking, the 'Propery ListEditor' launched, with which I could change the properties in this file. There are two properties, moduleName and modulePath. For moduleName I filled in 'Beach' and for modulePath I filled in '/System/Library/Screen Savers/Beach.slideSaver' (which I copied from the other user).
Now when I open the Preferences app and look at the screen saver, it doesn't crash anymore, even when I select the slide show.
[Editor's note: I believe I also fixed this same problem once by simply trashing any preference file I found that had "screensaver" in its name. The above is a more elegant solution ;-). In addition, if you have a bad module that's causing the crash, this problem will continue to occur until you remove the offending module from ~/Library/Screen Savers.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020425002730467