on Mac OS X Tiger 10.4 and unable to update rubygems from 1.0.1 to 1.3.5

Here's the command line story...

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computer-says-no:/ d$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.0.1 (1.0.1)
  - RUBY VERSION: 1.8.6 (2007-03-13 patchlevel 0) [i686-darwin8.10.1]
  - INSTALLATION DIRECTORY: /usr/local//lib/ruby/gems/1.8
  - RUBYGEMS PREFIX: /usr/local/lib/ruby/site_ruby
  - RUBY EXECUTABLE: /usr/local//bin/ruby
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-darwin-8
  - GEM PATHS:
     - /usr/local//lib/ruby/gems/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://gems.rubyforge.org

computer-says-no:/ d$ sudo gem update --system
Password:
Updating RubyGems...
Bulk updating Gem source index for: http://gems.rubyforge.org
Attempting remote update of rubygems-update
Successfully installed rubygems-update-1.3.5
1 gem installed
Installing ri documentation for rubygems-update-1.3.5...
Installing RDoc documentation for rubygems-update-1.3.5...
Could not find main page README
Could not find main page README
Could not find main page README
Could not find main page README
Updating version of RubyGems to 1.3.5
Installing RubyGems 1.3.5
ERROR:  While executing gem ... (NoMethodError)
    undefined method `ruby_version' for Gem:Module
setup.rb:36: uninitialized constant Gem::SystemExitException (NameError)

computer-says-no:/ d$ sudo gem install rubygems-update
Password:
Bulk updating Gem source index for: http://gems.rubyforge.org
ERROR:  Error installing rubygems-update:
        hoe requires RubyGems version >= 1.3.1

computer-says-no:/ d$ sudo gem install rubygems-update -v=1.1.1
Bulk updating Gem source index for: http://gems.rubyforge.org
Successfully installed rubygems-update-1.1.1
1 gem installed
computer-says-no:/ d$ sudo update_rubygems
Error: Cannot find RubyGems Update Path!

RubyGems has already been updated.
The rubygems-update gem may now be uninstalled.
E.g.    gem uninstall rubygems-update
computer-says-no:/ d$ gem -v
1.0.1

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any ideas much appreciated?
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