How to install rmagick gem on Windows?-Collection of common programming errors

How do I install rmagick gem for Windows XP? I already installed ImageMagick with the header files, and I installed RailsInstaller.org which comes with DevKit. I don’t know where to look to fix these errors.

C:\RailsInstaller\ImageMagick-6.8.2-Q16>ruby -v
ruby 1.9.3p125 (2012-02-16) [i386-mingw32]

C:\RailsInstaller\ImageMagick-6.8.2-Q16>gem -v
1.8.16

C:\RailsInstaller\ImageMagick-6.8.2-Q16>path=%PATH%;C:\RailsInstaller\ImageMagick-6.8.2-Q16

C:\RailsInstaller\ImageMagick-6.8.2-Q16>identify
Version: ImageMagick 6.8.2-0 2013-01-24 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2013 ImageMagick Studio LLC

C:\RailsInstaller\ImageMagick-6.8.2-Q16>gem install rmagick
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing rmagick:
        ERROR: Failed to build gem native extension.
        C:/RailsInstaller/Ruby1.9.3/bin/ruby.exe extconf.rb
checking for Ruby version >= 1.8.5... yes
Invalid drive specification.
Unable to get ImageMagick version
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=C:/RailsInstaller/Ruby1.9.3/bin/ruby


Gem files will remain installed in C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rmagick-2.13.1 for inspection.
Results logged to C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rmagick-2    .13.1/ext/RMagick/gem_make.out



C:\RailsInstaller\ImageMagick-6.8.2-Q16>dir include
 Volume in drive C has no label.
 Volume Serial Number is F8E5-EDB8

 Directory of C:\RailsInstaller\ImageMagick-6.8.2-Q16\include

01/29/2013  04:33 PM              .
01/29/2013  04:33 PM              ..
01/29/2013  04:33 PM              magick
01/29/2013  04:33 PM              Magick++
09/05/2009  04:47 PM               419 Magick++.h
01/29/2013  04:33 PM              wand

Here is the contents of gem_make.out

C:/RailsInstaller/Ruby1.9.3/bin/ruby.exe extconf.rb
checking for Ruby version >= 1.8.5... yes
Invalid drive specification.
Unable to get ImageMagick version
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=C:/RailsInstaller/Ruby1.9.3/bin/ruby

Here is the contents of extconf.rb

require "mkmf"
require "date"

RMAGICK_VERS = "2.13.1"
MIN_RUBY_VERS = "1.8.5"
MIN_RUBY_VERS_NO = MIN_RUBY_VERS.tr(".","").to_i
MIN_IM_VERS = "6.4.9"
MIN_IM_VERS_NO = MIN_IM_VERS.tr(".","").to_i



# Test for a specific value in an enum type
def have_enum_value(enum, value, headers=nil, &b)
  checking_for "#{enum}.#{value}" do
    if try_compile(