1. I am going to assume you have Eclipse Helios installed
   
2. Now to install the "DLTK - ruby stuff" open Eclipse > help > install new software... and then install everything shown in this screenshot here with the URL http://download.eclipse.org/technology/dltk/updates/
   
3. Now you would think that would mean (or at least I did) that you automatically also get the ruby interpreter installed. But it doesn't. Eclipse mearly now has the abiltiy to support ruby application development. So go get the ruby interpreter installed, for windows just use the one click installer here
   
4. Now you have to let eclipse know about your new ruby interpreter which you installed. So open Eclipse > window > open perspectives > choose Ruby perspective. Now that you're in the ruby perspective, Window > preferences > ruby > interpreters > click SEARCH and you should be able to both see and put a check-mark in "ruby.exe". Great.
   
5. Last step - try it out.
   File > New > Ruby Project click through that and make a project.
   Add an empty ruby script to your project, File > New > Empty Ruby Script and write in puts 'yipeee ruby is working in eclipse'
   Click on Run As and select "ruby script"... in the consile you should see the message yipeee ruby is working in eclipse
   

... and then install everything shown in this screenshot here with the URL