I\'m having this problem with nokogiri\'s gem:
Could not open library \'C:\\Ruby187\\lib\\ruby\\gems\\1.8\\gems\\nokogiri-1.4.6-x86-mingw32\\ext\\nokogiri\\libxml2.d
wow, i found the solution, there is a nokogiri for 64bits
goto rubygems, goto nokogiri gem, and look at the version list!
https://rubygems.org/gems/nokogiri
notice the x64-mingw32 and x86-mingw32 version
took me hours to figure this out...
You need DevKit to compile the gem properly.