Yup that line is the problem, the GMA cards are a pain when you need gaming performance. The good news is the newer MacBooks have a better 9400 card that allows you to play newer games like BioShock on medium settings.
Then again if you want to be gaming spending a little more money on a machine with a good card is worth it as it means you Mac will stay playable for that little bit longer. Although buying a MacPro is a little overkill
Edwin