You need to find out what graphics processor you have to download the correct driver. Download GPUZ from here;http://www.techpowerup.com/gpuz/
that will identify your graphics card make and model. ATi and Nvidia are the two main add in card manufacturers but you could also be running onboard video from another manufacturer like Intel for example.
Once you know what make and model your graphics chip is you can then go to that manufacturer's website to download the correct Win7 driver.