How to get a better graphics card for my desktop. I want to play godfather 2. read carefully below?

It says to play i need a Direct X 9.0C Compatible Video Card Shader Model 3.0 required. It says video card must be 256mb or more and contains one of these chipsets: NVIDIA Ge Force 6800, ATI X1600 Pro, or better. My Computer says i have a Intel GMA 3100. I want to know what number 1 where i can buy this certain graphics card that i need that i explained below. and 2 what type of place could take it to to get it put in or if i can put it in myself and how.