I had the same problem this morning. The Finder was going on and off, on and off, ... Really annoying, although all other apps were running fine. I first had to force reboot in order to log into another account under the other administrator password (I have set up two accounts with admn privileges). The Finder was working fine there. I thought immediately it had to do with some Finder prefs or plist files corrupted in my Library. I tried Disk Utility from the other account. Did not work. I tried Disk Utility from the Panther Start Up Disk. Did not work either. Whenever I tried to log in my main account the Finder refused to launch or was quitting after a second. I just didn't want to fiddle with Terminal which scares the shit out of me (anyway, never knew what to do with that beast).
My solution was to reboot under Classic. The Finder was obviously working fine there (OS 9.2.2). I deleted from my User Library, the localised.something file found on the Desktop, and the Pref files in the Finder (including .plist files). Rebooted from OS 10.3.6, logged back in my session and voilà! Everything back to normal.
Hope it'll help you.