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.
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.