If you want to try out b2g-desktop on windows then try the installer at https://github.com/downloads/sihorton/b2g-desktop-profile-installer/b2g-gaia-desktop.exe or the portable version https://github.com/downloads/sihorton/b2g-desktop-profile-installer/b2g-portable.exe.
This repository contains a pre-compiled gaia profile made from https://github.com/mozilla-b2g/gaia/ using the compilation instructions from https://developer.mozilla.org/en/Mozilla/Boot_to_Gecko/Building_Boot_to_Gecko. This compilation was performed on a ubuntu machine and the results added to this repository so that it can be used by windows machines.
Updating the repository:
To update the repository to include latest version of gaia follow the instructions at https://developer.mozilla.org/en/Mozilla/Boot_to_Gecko/Building_Boot_to_Gecko on linux or mac. The make step will create a profile directory. Copy the contents of the directory into this repository.