Forza Horizon (2012) features a system that detects save data from previous Forza Motorsport titles on your Xbox 360 hard drive. Unlike standard career progression where you must earn credits to purchase vehicles, these rewards are gifted directly to your garage as soon as you reach the first Festival hub, provided you have reached a specific "Driver Level" in the qualifying games. Eligible Games and Rewards

You cannot simply drag and drop a USB stick. Xbox saves are encrypted with a User ID.