First I tried the newbie guide exactly step-by-step with the file that I already had, but it still gave me the same error at the same point. I re-downloaded it from the PlaneShift downloads page and tried again, and it worked that time. Yay!
In case it comes up again for anyone else, I was originally using the torrented file, which was giving me the error, but when I downloaded it through the Uniquity mirror, it ran fine.
Thanks for your help, both of you!