Try Ruby in the Browser
There's a pretty awesome online "Ruby in your browser" tutorial that you could try. It has a built in Ruby console and everything is interactive. It's takes 15-30 minutes or so to go through, and it's good. Someone put a whole lot of effort and love into making this one for us Ruby newbies. Go check it out, but use a FireFox browser, because I couldn't make it work properly in IE in Vista.
http://tryruby.hobix.com/