> I'm new to Ruby but am fairly experience in using TDD with Java and am
> having some problems in converting my knowledge over.

I strongly recommend a look a rspec at http://rspec.rubyforge.org which
is a behavior driven development framework (BDD). I learned of it from
Josh's RubyOnRails PodCast, another highly recommended resource. 

I can honestly say I actually enjoyed writing a spec and test suite with
it. They have converters that will also take the natural language from it
and generate a 'manager-friendly' document outlining all the
specification, just so cool--especially to those of us pushing Ruby hard
in the enterprise.

> I'm using the Eclipse Ruby plug-in and want so organise my test source and
> code source files separately as I do in Java.

Rspec hasn't made into the RadRails plugin yet, and there has been talk
about it on other threads. From the buzz rspec is generating I would
bet it will become core or stdlib soon.

> Ideally a tutorial would be available but I'm sure the above is available
> somewhere but I can't find it!

They have a tutorial on the rspec site.

Enjoy.

Rob