zlibのインストール

zlibがないとおっしゃっているので、zlibをダウンロードして%RUBY_HOME%\binに配置する。そして、gem list!

>gem list
C:/ruby/lib/ruby/1.9.1/rubygems/spec_fetcher.rb:1:in `require': 193: %1 は有効な Win32 アプリケーションではありません。   - C:/ruby-1.9.2-p0-x64/bin/zlib.so (LoadError)
        from C:/ruby/lib/ruby/1.9.1/rubygems/spec_fetcher.rb:1:in `'
        from C:/ruby/lib/ruby/1.9.1/rubygems/commands/query_command.rb:3:in `require'
        from C:/ruby/lib/ruby/1.9.1/rubygems/commands/query_command.rb:3:in `'
        from C:/ruby/lib/ruby/1.9.1/rubygems/commands/list_command.rb:2:in `require'
        from C:/ruby/lib/ruby/1.9.1/rubygems/commands/list_command.rb:2:in `'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:140:in `require'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:140:in `rescue in load_and_instantiate'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:132:in `load_and_instantiate'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:65:in `[]'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:118:in `find_command'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:104:in `process_args'
        from C:/ruby/lib/ruby/1.9.1/rubygems/command_manager.rb:75:in `run'
        from C:/ruby/lib/ruby/1.9.1/rubygems/gem_runner.rb:39:in `run'
        from C:/ruby/bin/gem.bat:32:in `
'

えっと、zlibも64bit版入れろや、ゴルァ！！ということらしい。
下記から64bit版のzlibをダウンロードして配置。
http://www.winimage.com/zLibDll/index.html

で、gem list！！
めでたくＯＫ

ついでにsinatoraもインストール。

>gem install sinatra
Successfully installed rack-1.3.0
Successfully installed tilt-1.3.2
Successfully installed sinatra-1.2.6
3 gems installed
Installing ri documentation for rack-1.3.0...
Installing ri documentation for tilt-1.3.2...
Installing ri documentation for sinatra-1.2.6...
Installing RDoc documentation for rack-1.3.0...
Installing RDoc documentation for tilt-1.3.2...
Installing RDoc documentation for sinatra-1.2.6...

OK