Honestly, if you're planning on focusing on Rails eventually, I'd start with the Rails Tutorial by Michael Hartl (http://ruby.railstutorial.org). It's easy to get lost as a total beginner with all the various things Ruby itself is capable of, when you might have better results focusing on a smaller subset of the whole, at least to start. Rails tutorial also has a chapter early on (one of the first five) that contains an intro to ruby and can point you in the right direction from there.
If you have previous programming experience, I don't think that it matters much. You can always look stuff up as you go if you already know enough to know what you're looking for.
Stackoverflow is a great resource. The link below is has details on Rails (maybe not best starting point for Ruby) but helpful site to learn and find good resources.
Highly recommend this free 5 week Coursera course out of UC Berkeley. All development is in Ruby and Rails. There is some introductory Ruby material - you don't need to have any prior knowledge. It started last week, but you can join late without a problem.
I wonder what the intentions of these universities are by offering these courses for free. (seriously) hm...
It might just be me being a pessimist, but they have to have some kind of evil motive, right? It seems unheard of that any university offers something for free.