Oh, it probably requires Rails 1.2
The plugin is about 10 lines of code! the rake task will install it just fine. The only thing that changed was how the plugin sets up the lib paths. Use svn and rollback a few times and find a good revision:
http://bs.techno-weenie.net/!history/2660/plugins/gems?stop_revision=0
1177 should be fine for rails 1.1.6
http://bs.techno-weenie.net/!source/1177/plugins/gems/init.rb