Hi,
I'm a 30 years old french player (sorry for my poor english) and I've troubles with AC2 in dual monitor mode (2 x 1680 x 1050)
In the game (and not ony in the menus), it displays a single image (1680x1050 sized) in the center of my two monitors with black background on the left and on the right.
I've played others games which work perfectly with dual monitor mode (Mafia II, Burnout Paradise, Avatar, GTA IV, DiRT 2)
For information, my graphic card is a MSI Radeon HD5870.
Thank you for your help !
How far into the game did you get? From memory, it stayed in single screen mode through the cut scenes and the early tutorial, and only went to the full widescreen once you started the training part in the animus. Sometimes it can take a few seconds to transition to the full widescreen too.
Just do a double-check of the resolution settings in the game, and then make sure you get into the story a bit. If you are still on a single screen after half an hour, I assume something isn't right but hard to diagnose remotely.