Rspec --help gives undefined method 'Pathname'

Trying to setup environment on xandros linux.
running ruby 1.9
gem 1.3.7

sudo gem install rspec

but when I issue rspechelp
I receive the following
/usr/lib/ruby/gems/1.9/gems/rspec-core-2.0.0/lib/rspec/core/ruby_project.rb:31:in
ascend_until: undefined methodPathname for
RSpec::Core::RubyProject:Module (NoMethodError) from
/usr/lib/ruby/gems/1.9/gems/rspec-core-2.0.0/lib/rspec/core/ruby_project.rb:27:in
find_first_parent_containing from /usr/lib/ruby/gems/1.9/gems/rspec-core-2.0.0/lib/rspec/core/ruby_project.rb:23:indetermine_root

Any help greatly appreciated.