Failed DataMapper Gem install on Win7 - windows-7

Question

I'm learning to use Sinatra + Datamapper to build a lightweight webapp.
I ran gem install sqlite3 datamapper dm-sqlite-adapter and it seemed to have successfully installed...
I then tried to execute my .rb file which starts with:
require 'sinatra'
require 'datamapper'
and I got an error that it could not find the datamapper file.
C:/Ruby192/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': no such file to load -- datamapper (LoadError)
I also tried with require 'data_mapper' since there is conflicting information on the internetz as to the correct spelling of that gem, but same result.
I then listed all my installed gems (see below) and realilsed that there is no such gem as datamapper or data_mapper. I read so,ewhere that it is a meta-gem, I guess that means it doesn't actually install that one gem but rather all the gems starting with dm- ?
As a last resort I tried gem install data_mapper
and I got the ill fated:
C:\Users\Manu\Sinatra>gem install data_mapper
Building native extensions. This could take a while...
ERROR: Error installing data_mapper:
ERROR: Failed to build gem native extension.
C:/Ruby192/bin/ruby.exe extconf.rb
creating Makefile
make
'make' is not recognized as an internal or external command,operable program or batch file.
Gem files will remain installed in C:/Ruby192/lib/ruby/gems/1.9.1/gems/json-1.6.4 for inspection.
Results logged to C:/Ruby192/lib/ruby/gems/1.9.1/gems/json-1.6.4/ext/json/ext/parser/gem_make.out
I searched all over and just couldn't find anything to help me troubleshoot this, so hopefully there's someone roaming this forum with a magic wand and a pointy hat!
Many thanks
PS: I'm running ruby 1.9.2p0 installed with the installer
* LOCAL GEMS *
abstract (1.0.0)
actionmailer (3.0.3)
actionpack (3.0.3)
activemodel (3.0.3)
activerecord (3.0.3)
activeresource (3.0.3)
activesupport (3.0.3)
addressable (2.2.6)
arel (2.0.6)
backports (2.3.0)
builder (2.1.2)
bundler (1.0.7)
cgi_multipart_eof_fix (2.5.0)
data_objects (0.10.7)
diff-lcs (1.1.3)
dm-aggregates (1.2.0)
dm-constraints (1.2.0)
dm-core (1.2.0)
dm-do-adapter (1.2.0)
dm-migrations (1.2.0)
dm-sqlite-adapter (1.2.0)
dm-transactions (1.2.0)
do_sqlite3 (0.10.7 x86-mingw32)
erubis (2.6.6)
fastercsv (1.5.4)
gem_plugin (0.2.3)
growl (1.0.3)
i18n (0.5.0)
json_pure (1.6.4)
mail (2.2.12)
mime-types (1.16)
minitest (1.6.0)
mongrel (1.1.5 x86-mingw32)
multi_json (1.0.4)
polyglot (0.3.1)
rack (1.4.0, 1.2.1)
rack-mount (0.6.13)
rack-protection (1.2.0)
rack-test (0.5.6)
rails (3.0.3)
railties (3.0.3)
rake (0.8.7)
rdoc (2.5.8)
rspec (2.8.0)
rspec-core (2.8.0)
rspec-expectations (2.8.0)
rspec-mocks (2.8.0)
rubygems-update (1.8.15)
sinatra (1.3.2)
sqlite3 (1.3.5 x86-mingw32)
sqlite3-ruby (1.3.3, 1.3.2 x86-mingw32)
sys-uname (0.9.0 x86-mingw32)
thor (0.14.6)
tilt (1.3.3)
treetop (1.4.9)
trollop (1.16.2)
tzinfo (0.3.23)
yard (0.7.4)

Answer 1

It seems the RubyInstaller Development Kit is missing:
http://rubyinstaller.org/add-ons/devkit/
The devkit installs a C-compiler (and some other stuff like make) to compile C-written parts.
Install it and try again to install the gem - perhaps with option --platform=ruby.
Details can be found at https://github.com/oneclick/rubyinstaller/wiki/Development-Kit