Recommended JRuby Install For JRubyArt
The preferred JRubyArt setup requires that you do a system install of JRuby. You should install java before attempting to install JRuby. Install at least version 126.96.36.199.
Alternative Setup For JRubyArt
It is possible to use JRubyArt without doing a system install, by using JRuby-Complete. You do need to install java and MRI ruby. However you will not be able to install certain gems with this setup.