Or, you may download the file.
One of the most difficult parts of the tech review for Learning Rails was Chapter 1, installing Rails. There are way too many operating systems and choices within those operating systems to provide a straightforward explanation.
To help deal with that problem, at least for some common operating systems and environments, I'm creating screencasts that show how to install Rails, demonstrating both how to do it and that it actually is possible. (Some folks really doubted that, though Ubuntu wasn't the hardest environment.)
This first screencast looks at installing Ruby on Rails on Ubuntu's Hardy Heron 8.04 LTS (Long-Term Support) desktop edition. It's a relatively painless install, as the package manager does most of the work. Just make sure you pick sqlite3 packages instead of sqlite - I burned myself good on an earlier take of this!
Update: If you're curious about the distinction between deploying software with apt-get and deploying with ruby gems, you might find this strongly-opinionated discussion interesting.
(And yes, I know - Ubuntu's already moved on to Intrepid Ibex (8.10), but Hardy Heron will be around for a long while. Let me know if you encounter any new problems with 8.10, here or at the Excursions on Rails page.)