Here is a link to help you find the prefs folder in Vista.
http://www.gnutellaforums.com/genera...der-vista.html.
Also before you changed the Java version, did you completly remove all versions of Java 1st?
I also read that someone had some Luck by uninstalling and reinstalling a fresh copy of limewire after the fixes above. If you do this, make sure you uninstall by going to START > All Programs > Limewire > Uninstall. This is the correct way to uninstall. Do Not go to Add/Remove Programs.
Hope this helps.