No kidding, all the card variations is ridiculous.

One of the big differences is pipelines. That means how many pixels your card will pain on the screen at one time. Your 9600 probably does 4. The 800 series and better will do 12 or more depending on the specs and settings of the game and card. This means speed.

Also, the cards are simply more powerful, faster, have more memory and are able to work with newer DX codes. Mind you, the Radeon cards don't do version 3 shaders, meaning in games like IL2-Pacific Fighters and Splinter Cell: Chaos Theory, you simply cannot access some of the game's highest graphics settings. This is a big one for the IL2 flightsim series because only the new Nvidia cards will allow you to use the "Perfect water 3" setting in the game which gives you incredible graphics of the ocean and waves. You can't get it with the ATI cards. Though the ATI cards are said to have overall better picture quality.