You can't install Windows on a removable drive.
But you can install it on the ssd under bootcamp, and then (if the installer of the game allows it) install the games on the external.
Kees
I am buying a MacBook Pro with a ss hard drive (which is small), it has the nvidia 1gb graphics card. I want to play many video games which require Windows, but most of these games take up quite a bit of space so I do not want to run bootcamp on the Mac ss.
Is it possible to take an external hard drive format the entire thing as a Windows 7 system and run this hard drive as an alternate with my computer for the use of video games? Also, I have USB 3.0 so it seems this would be the best connection for speed and price, am I right in thinking this?
Thanks in advance

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic