Didn't see any mention of the MS Java VM (only a suggestion on proxy setting for Sun Java VM). Just a thought on why long-term a Java enabled site does not work for you or your relatives newish PC. As I said a new PC will not have the MS Java VM installed.
As I mentioned, the Dulux (
www.dulux.co.uk) has a Java application (called MousePaint I think). Give it a try because if that works it at least proves MS Java VM working.