C:\Users\Luis>ruby -v
ruby 1.9.2p0 (2010-08-18) [i386-mingw32]

C:\Users\Luis>gem install mysql2 --platform=ruby -- --with-mysql-include=C:\mysql-5.1.51-win32\include --with-mysql-lib=C:\mysql-5.1.51-win32\lib\opt
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
Successfully installed mysql2-0.2.5
1 gem installed

C:\Users\Luis>irb
irb(main):001:0> require 'mysql2'
=> true
irb(main):002:0> client = Mysql2::Client.new(:host => "localhost", :username => "root", :database => 'foo_dev')
irb(main):003:0> results = client.query("SELECT COUNT(id) FROM users")
=> #<Mysql2::Result:0x2bd9148>
irb(main):004:0> results.map { |r| r }
=> [{"COUNT(id)"=>0}]