以下はエラーログです。
$ jruby -S gem install ruby-debug-ide -v '0.4.16'
Building native extensions. This could take a while...
ERROR: Error installing ruby-debug-ide:
ERROR: Failed to build gem native extension.
"c:/Program Files/jruby-1.6.6/bin/jruby.exe" mkrf_conf.rb
""c:/Program Files/jruby-1.6.6/bin/jruby.exe"" -rubygems c:/Program Files/jruby-1.6.6/lib/ruby/gems/1.8/gems/rake-0.9.2.2/bin/rake RUBYARCHDIR="c:/Program Files/jruby-1.6.6/lib/ruby/
gems/1.8/gems/ruby-debug-ide-0.4.16/lib" RUBYLIBDIR="c:/Program Files/jruby-1.6.6/lib/ruby/gems/1.8/gems/ruby-debug-ide-0.4.16/lib"
'""c:' is not recognized as an internal or external command,
operable program or batch file.
Gem files will remain installed in c:/Program Files/jruby-1.6.6/lib/ruby/gems/1.8/gems/ruby-debug-ide-0.4.16 for inspection.
Results logged to c:/Program Files/jruby-1.6.6/lib/ruby/gems/1.8/gems/ruby-debug-ide-0.4.16/ext/gem_make.out
編集:Ruby on Rails 3 (JRubyではなく)で同じことを試してみたところ、同じエラーが発生しました。