After installing Kubuntu 9.04 I checked for NetBeans version in repository – and it was 6.5.
So now official way of installing NetBeans 6.5 is:
sudo apt-get install netbeans
This will install NetBeans and a lot of dependencies. After download and installation are finished, you will have NetBeans properly installed on your computer.
This means that manual installation as described before is discouraged, at least until NetBeans 6.7 is released.