Working on this right now I'll check the guide once my date is lower then 1tbI would re size the 2tb partition down so that it will fit inside the 1tb drive then follow the steps that are in this guide that spynoodle wrote
http://www.computerforum.com/189534-how-clone-hard-drive.html
Those would all work for cloning the drive. But he asked if he can move just the OS over to the new hard drive. Only way to do that would to reinstall windows to the new drive.