Dual screen with the Sims 3

No one?

A game has to be specifically programmed to use more than one screen. You can probably use your display drivers to clone one monitor to get the game to appear on both screens, but you wont be able to control them independently.

Looking at that setup it's probably done using custom software. I'm not aware of the Sims 3 having native support for multiple monitors so I'm guessing it's something he setup on his own. Basically if you want to do it you'll probably have to figure it out on your own to some degree and will probably require some programming to make your system recognize the two monitors as one and display in the appropriate resolution. Also using two different monitors with two different sizes while both make it more difficult and not look that great. Honestly probably not worth it.