Some package provides vim-ruby on Ubuntu, for example vim-nox.
simply:
sudo apt-get install vim-nox;
will get you vim with ruby, as well as compiled in “support for scripting with Perl, Python, Ruby, and TCL but no GUI.”
sudo apt-get install vim-rails
will install a “selection of vimscripts that make editing Ruby on Rails applications extremely easy.” but as it depends on vim-full and vim-addon-manager, it will also install the vim-gnome version of the GUI, that is “a version of vim compiled with a GNOME2 GUI and support for scripting with Perl, Python, Ruby, and TCL.”