Installing rbx-2.0.0-dev with Ruby 1.9 support using rbenv can be a tad tricky. This is what I did to get up and running, you'll need another version of ruby already installed as well as rake.
The basic outline:
- Clone Rubinius HEAD from github
- Configure installation for rbenv and 1.9 support
- Install Rubinius
- Configure your $PATH to use Rubinius gems
- Start using Rubinius