Ah, that would be why. You wont get anywhere near the required graphics processing power with a built-in solution like that. You definitely need to invest in a discrete card to be able to handle D3's requirements.
The 9800 mentioned above is a pretty decent and cheap option. I'm currently using the nvidia 480, which I see is down to only about $200 if that's in your price range. It's been pretty good for me so far.