Ok, I'm probably going to feel dumb when I find out the answer to my questions, but it's the only way I'll learn...

I'm running Fedora Core 2 and using Mozilla Thunderbird as my Email Client. I would like to be able to use Thunderbird for Hotmail & Gmail, so, I have downloaded the latest MrPostman Jar file (and additional scripts for Gmail). Now, the documentation says to use the Java command to install the app, but whenever I type java in the terminal, bash tells me it is an unknown command.

What am I doing wrong and how can I get this working?

Thanks

You'll need to install a java runtime. You can try those that comes with your distribution or get it from http://www.javasoft.com

You might want to search around LQ for suggestions for which to install. I've seen quite a few of these. I personally use the one from sun.

I have j2re (sun's java runtime) but it still wont work.
Is there something in the configuration of Java that I need to fix?

I think you have to set the path to the jre bin or create the links yourself (maybe in /usr/local/bin). At least this is the case for the non-rpm version.
This question has been answered many times, including how to get the plugin working for browsers, so you might want to search for them.