Thanks again for the info, sminchom. Would you be able to provide the following details too?

Open Terminal (Applications -> Utilities -> Terminal) and type "java -version" without the quotes. What does it say?

What does the installer log (available from the installer after installing, but before closing, under File -> Log I think) say? (Make sure you tell it to display all information.)

Apple has released an update to Java, available at http://www.apple.com/downloads/macosx/apple/java.html . You may want to try downloading and installing the update. PLEASE PLEASE PLEASE gather the above info before installing the update, though.

Sorry for the lots of stuff to do... it's an elusive problem. Thanks very much for your help!