I just got finished updating my Rails setup script and testing it on the Alpha 3 version of Lucid. Now that the packages seem to be settling down the the repositories for Lucid suddenly I can find the ones I need for Rails. The script now gets Rails 3 running on either Karmic or Lucid. If you need older versions of Rails just uncomment the lines for the version you need.
You can get the latest version of the script here: http://github.com/sleepycat/wrong-side-of-the-tracks