To see how to install Cordova on Windows with Visual Studio, go here.

After you created the Cordova app using the generated Template in Visual Studio, you must use the plugman package instead of the cordova tool to install plugins. If you didn’t install plugman, first install plugman using npm.
>npm install -g plugman

To add the plugin camera use the following code inside the root of the solution.
C:\>cd \dev\mobile\CordovaWP7_3_4_0_App1
C:\dev\mobile\CordovaWP7_3_4_0_App1>plugman install --platform wp7 --project CordovaWP7_3_4_0_App1 --plugin org.apache.cordova.camera
Fetching plugin "org.apache.cordova.camera" via plugin registry
Starting installation of "org.apache.cordova.camera" for wp7
Preparing wp7 project
org.apache.cordova.camera installed on wp7.