OK, so I went to the SL Wiki to find out how to build the SL client, and decided to use subversion to retrieve the code. Ah, there's the command, and I fill in which version I want.
Which version do I want? Well, I hope I'll be able to try out the version with shadows, but for now, I want the current version. I looked at the page explaining about the source branches... oh, OK. I want the current release version, so I typed the command and asked for release... yeah, that's the ticket!
Good thing I haven't used much of my 500 GB hard drive. :)
(Actually, it's not that bad; just a couple of gigabytes of source, and I will be pruning a bunch.)