It does work though, thats the issue. They list compatable cards, ones that support the graphics APIs that they use. The x300 does. I would bet that in a Dual Core AMD 64 system, with some decent ram, it would run ok. There is no way possible that they can tell you which cards will require which amount of power from the system.
Plus, lowering some of the options would yeild alot of performance...i would bet turning off the shadows would give you a 10-15fps boost...their shadow rending is terribly ineffecient.
Im not saying that the game shouldnt run better on that card, or any other one, it should. There isnt enough on the screen at any time to justify the numbers that i get out of mine. I stay around 45-50 on my laptop, but i can run F.E.A.R at well over 70 with much better graphics. If this engine was packaged into a top-shelf game today, many people would lose their jobs, as its terribly machine hungry. But hey, we're only paying $200 for a game, why should we complain right, i mean, they're practically giving it away.
Basically, G3 is the best sim out there overall, sadly though, the bar is pretty low, so the best isnt saying much...