rails2.0.1は RubyGems >=0.9.4

ということで、update gemをupdateする場合は、「gem update --system」というように「--system」オプションを付けるんだね。

Rails requires RubyGems >= 0.9.4 (you have 0.9.2). Please `gem update --system` and try again.

% sudo gem update --system                                                                                 
Updating RubyGems...
Bulk updating Gem source index for: http://gems.rubyforge.org
Need to update 10 gems from http://gems.rubyforge.org
..........
complete
Attempting remote update of rubygems-update
Successfully installed rubygems-update-0.9.5
Updating version of RubyGems to 0.9.5
Installing RubyGems 0.9.5
・・・・
・・・・
・・・・
As of RubyGems 0.8.0, library stubs are no longer needed.
Searching $LOAD_PATH for stubs to optionally delete (may take a while)...
...done.
No library stubs found.
RubyGems system software updated

ruby界隈はupdateが早くて追従するの大変ですね。こりゃ。