ATI driver refers to the driver (a driver is simply a piece of software) for your computer's video controller. If you don't have a CD with the driver on it to re-install, you can go to the ATI website and download one. You must know the model of your video controller in order to get the right driver for it. First download a free utility to identify it from here: Everest Home Edition:
http://www.lavalys.com/products/over...ng=en&pageid=1
Then go here and look for it's driver:
http://www.atitech.com/