Installing a 64bit operating system would definitely improve performance. Maybe not a lot, but it would.
But it could be too time-consuming just to make the game run more fluently.
A GTX560 should run the game at least as fluent as shown in the video. If not, then it is not the fault of the graphics card.
You should also try to adjust the screen resolution. The smaller the screen resolution, the more fluent the game should run.
