Where can I find the video drivers for my computer?

I have a Dell Inspiron 531 with unaltered hardware, so I have the same video card that I got from the factory and it hasnt been changed. My problem is that when I had Windows Vista I used to play a video game, but now that I installed Windows 7 the same video game looks choppy. Everything else is ok, video plays ok, etc. Does anyone know how can I solve this problem or where to find the drivers that I need?