It's frustrating, since I only bought the computer a couple months before the game came out in the first place, you'd think they'd be using comparable hardware when they designed it.
Integrated cards are typically weak, though; it's not like that card was top-of-the-line when it came out. It's enough to play some older stuff and newer games with low graphic requirements (like Dishonored and Mass Effect 3), but we're talking about a game that would likely make a "top three most GPU-straining games in existence" list.
EDIT: It's worth mentioning that the game was (allegedly) playable with that card before the Enhanced Edition update, though only on the lowest settings and with a resolution of 800x600. I think the person who did that also used some background programs that helped, and even then they only got 20-24 FPS. Point is, it was technically possible back around the game's initial release. The Mac version is pre-patched to the Enhanced Edition, though, so that's not possible anymore. The EE made it more difficult to run, sadly.