The following instructions will install Vim with the Ruby interpreter and Command-T. I keep my vim settings under revision control, thus I have chosen to use Git's submodules and Pathogen to manage Command-T. Depending on your preferences, you may want to setup Command-T differently. I recommend reading through the Command-T Readme
sudo apt-get install ruby ruby-dev libncurses5-dev mercurial clone build-essential rake
I chose to compile vim with my system Ruby, 1.8.7. It is important that you use the same version to compile both Vim and Command-T. If your using RVM and you want to do the same, before proceeding you will want to:
rvm use system