The last few lines of the help read:
  Generator gems are also available:
    1. gem list generator -s http://gems.rubyonrails.org
    2. gem install login_generator -s http://gems.rubyonrails.org
    3. script/generate login
Problems:
  * "gem list -s http://gems.rubyonrails.org"  doesn''t do
what
    you expect.  -s is not a valid flag; you need --source.  The full
    correct command is
       gem list -r -s http://gems.rubyonrails.org
    The -r is necessary to make gems look remotely.  I''ve raised this
    issue with RubyGems developers; --source should be sufficient, and
    a -s abbreviation of --source would be nice.  [I''m ignoring the
    "generator" argument for now; see next point.]
  * The command "gem list generator" lists gems whose name _starts
    with_ "generator", so it will not show the
"login_generator" gem.
    Use the "search" command.
  * Even if it _did_ show the login_generator gem, there''s no such gem
    on that server to show!
Summary:
  * Change the command to
       gem search -r --source http://gems.rubyonrails.org
  * Put the login_generator gem on that server!
Sorry for the long-windedness.
Gavin