Do you have any log in items? If so disable them. You can do it via the pref pane or by holding down "shift" at start up.
Also try holding down the command+V keys at start up. This will alow you to see what is going on at boot up and hopefully show if any errors are occurring at boot.
If that does not work, create a new user in the system prefs and see if the Finder launches. If it does, I would bet it is a bad pref somewhere, if not "com.apple.finder.plist" then most likely from one of the last applications or drivers that were most recently installed.
Jim
P.S. Do you have OS 9 installed? If the above suggestions don't work you may need it if you are not too familiar with the Terminal.
