New to Java

I have just started using Linux 9.0, and immediately installed the Firefox Web Browser and to get the best out of this installed j2re-1_4_2_06, made the link to the plugin as required and found Firefox did not seem to recognize it. I then tried to install Limewire and was informed that I could not as no jvm was installed.
I upgraded to jre-1_5_0_01 and did the same with the plugin after deleting the one installed at my previous atempt and Firefox will not start at all in the desk top and if run in a shell it just opens a shell window and closes it again. I tried to install Limewire again and was told the same no jvm message.
Can someone help please?