This installs a patched ruby 1.9.3-p429 with the railsexpress patchsets from https://github.com/skaes/rvm-patchsets
You will also need a C Compiler. If you're on Linux, you probably already have one or know how to install one. On OS X, you should install XCode, and brew install autoconf
using homebrew.
curl https://raw.github.com/gist/5693603/rbenv.sh | sh ; rbenv global 1.9.3-p429-railsexpress