I do something vaguely like that. I've got a dual boot OS X and Windows XP Mac mini, and I have two USB keyboards hooked up to it. When using my 'real' computer (the OS X side), I use an Apple keyboard with the keycaps moved around (the keycaps on an Apple keyboard are all identical, so there's no terrible jagged bumpy look). When using the 'toy' computer for playing old PC games, I use an IBM keyboard with QWERTY keycaps and layout instead. This saves me the trouble of constantly remapping 'WASD' to 'WARS' and keeps me from forgetting how to type on the 'average' keyboard.
This is, of course, totally unlike the setup that the original poster had in mind. In OS X, switching layouts can be done on the fly with just two clicks on a menu item in the system tray equivalent - I used to use this shortcut from time to time while using the QWERTY keyboard in OS X before I regained my old QWERTY speed in Colemak - but I have no idea if Windows has a similar feature, since literally the only thing I ever do in Windows is double click on a desktop icon to start a fullscreen game.