Difficulties install Rspec

I recently purchased the beta of the Rspec PragBook, and am really
looking forward to diving in. Unfortunately, I’m having difficulty
installing Rspec. I’m currently running Ruby 1.8.7 on Snow Leopard
(10.6.4). Both Ruby itself, and Gem, appear to be working fine.
However, the following is displayed whenever I attempt to install

~$ sudo gem install rspec --version 2.0.0.beta.19

Thank you for installing rspec-core-2.0.0.beta.19
Please be sure to look at Upgrade.markdown to see what might have
since the last release.

Thank you for installing rspec-expectations-2.0.0.beta.19

Thank you for installing rspec-mocks-2.0.0.beta.19

ERROR: Error installing rspec:
rspec requires rspec-core (= 2.0.0.beta.19, runtime)

What I find really weird is that rspec-core seems to install at the
beginning of the process, but then can’t be found at the end.

I did a quick scan of the archive and didn’t see anything addressing
this problem. (My apologies if I missed it.) Any help would be
greatly appreciated.