problem installing java6 on ubuntu 9.04

I recently installed java6 hoping to run java on firefox. However, there seems to be some problems as the icon on the menu doesn't run (>Applications>Internet>Sun Java 6 Web Start).

So I did some research on the net and follow the instruction using Terminal to configure it. Here's some error message I got:

1. I am sure that java6 is installed on my system, because I type the command $ java -version, and it shows:
  "java version 1.6.0_13"

2. however, when I try to configure it with the command $ sudo update-alternatives --config java, it shows:
  "There is only 1 program which provides java
(/usr/lib/jvm/java-6-sun/jre/bin/java). Nothing to configure."

3. and, when I use command $ sudo update-java-alternatives -s java-6-sun, here is the error message I get:
  "No alternatives for firefox-javaplugin.so.
No alternatives for iceape-javaplugin.so.
No alternatives for iceweasel-javaplugin.so.
No alternatives for midbrowser-javaplugin.so.
No alternatives for mozilla-javaplugin.so.
No alternatives for xulrunner-1.9-javaplugin.so.
No alternatives for xulrunner-javaplugin.so."

4. when I use the command $ sudo vi /etc/jvm to open JVM, the screen is empty.
I follow instruction to type /usr/lib/jvm/java-6-sun, the following error appears:

"E486 Pattern not found: usr"

Can anyone help me to fix this?

Thanks a lot.

Bill