Fedora core 4, FireFox and Java

I have just installed Fedora Core 4 on a computer at home.

It has FireFox 1.0.4 on it and I want to use the java runtime to work
with it.

Java is installed on the computer as well.

The version of Java is 1.5.0 and the plugins for it are stored in the
following folder:
/usr/java/jre1.5.0_04/plugin

Firefox is installed in:
/usr/lib/firefox-1.0.4/

According to the online help, all I should need to do is run the
following from the plugin directory on the firefox folder:
ln -s /usr/java/jre1.5.0_04/plugin/i386/ns7-gcc29libjavaplugin_oji.so

I have done this, and I have made sure that the Enable Java option is
selected on in the firefox preferences window.

However, if I try to run a site that uses the Java plugin, I get the
following:
The site displays a jigsaw piece and a 'click here to download the
plugin'

When I click on the link, a new window appears saying that the Java
Runtime Environment is available.  I click next and a new window
appears saying that FireFox has installed the missing plugins but the
Java Runtime Environment is not available and it has a manual install
button beside it.

Can anyone please help and tell me what I have missed?  This is driving
me nuts at the moment.

Thanks in advance.
Dave.