what does a graphics card do?
in order to play a game smoothly, the computer must be able to update the picture on your screen at least 30 times per second(30fps-frames per second). 60fps is very good. todays games use high detail objects with high detail textures on them that give them the final look, as well as some advanced lighting effects. the object detail is handled by the cpu(hope you know what that is!), this is handed over to the agp card which applies the textures and renders the final picture with lighting which is sent to your display. this requires a lot of computation, so the agp card is there to help the cpu, resulting in a higher fps and smoother gameplay.