This is how I loaded Topojson into my Windows 7 machine

Topojson install

1. Install Anaconda to get your python 2.7.
2. Install .Net Framework - dotNetFx45_Full_setup.exe
3. Uninstall the Microsoft Visual C++ 2010 instances.
4. Install the Microsoft SDK - winsdk_web.exe
5. Install Node.js - http://nodejs.org/download/
6. Open your command prompt as an administrator 
  >Start
  >"cmd" in Search for All Programs
  >Ctrl-RightClick on CMD and "Run as Administrator"
7. Set your environment for the SDK (this was tricky to figure out!)
  > call "C:\Program Files\Microsoft SDKs\Windows\v7.1\bin\Setenv.cmd" /Release /x64
  (This is for 64 bit.  For 32 bit use "/x86" instead of "/x64" in the above)
8. Install your Topojson from NPN
  >npm install -g topojson

> topojson --id-property BASIN -p name -o Basins_topo.json Basins.geojson <
  1. --id-property - <The unique ID field?>
  2. -p name - <list fields to bring over.  "" will return all fields>
  3. -o - <the name of your output file - I use *_topo.json to differentiate from *.json and *.geojson>
  4. Finally the input file.)

Thanks a lot! It really helped me.

I have created an extensive German tutorial about have to install topoJSON/contextify and for sure node-gyp on a Windows system. I hope it is as detailed as possible and some of you can now manage to install it. Because it is in German I added as many pictures as possible. Hope you like it: **http://www.kwoxer.de/2015/01/26/topojson-contextify-node-gym-unter-windows-installieren-tutorial/**ow