Hey, thanks guys, and sorry for the trouble.
xinit 5 gave me the same problem, but I discovered something strange. The footswitch on my computer wasn't working, so I tried moving it with my hand and pressing the buttons, and it worked!
Okay, not really that stupid, but apparently the failsafe thing hadn't crashed, just that it wasn't working with NumLock on. After turning that off, I was able to go into KDE, only to find that things still weren't completely back to normal.
But after deleting $HOME/.scim and another SCIM-created directory under $HOME/.gconf/apps, I was able to uninstall and reinstall SCIM with no problems, and, as a bonus, I (perhaps crazily) reinstalled the Cooker RPM that had given my trouble in the first place, this time with --nodeps (I figured that some of the dependencies I had also installed had been the root cause of my problems), and lo and behold, that now works perfectly too.
So everything is better than before. Thanks again!
Now on to my next post. This one will be less urgent.