First a couple caveats: You need to install Bluestacks if you haven't already. You can find that here:
Bluestacks is pretty great. Installs like any other Windows app. Try playing Draw Something using a mouse... lifechanger.
Once installed, you need to install an Android app that will allow you to backup other Apps. I chose ES File Explorer because it can do this and connect back to the computer to transfer those backed up apps to the desktop. There are other apps you can use and if you choose to do so, write us up an instructable doin' it your way. :)
Follow your nose and use the pictures here as a reference. Once you get past the third screen here, it's like installing an Android app on anything else.