Aah, that explains why I couldn't find the pref file in the installation folder then!
That seems to have done the trick, at least the .jar loads now. Would be nice if the .exe file worked though, but it doesn't seem to like the jvm.dll file in the " jre\bin\server " folder.
Hopefully this helps, at least it'll help me. Finding issues like this will give me clues in what to look for when I finally decide to produce my own games.