NVidia GeForce 8600 GT 256mb I really didn't see a reason why it would be 512 mb's as the game isn't very graphically intensive as far as I saw.
Not a Radeon then.
The fact that the game doesn't "look" like it needs 512MB of graphics doesn't mean it's well optimized. Maybe it was tested (and optimized) more for Nvidia drivers than for Radeons. Maybe the drivers for the 8600GT handle video memory better than the drivers for the HD 2400. According to gpureview, the 8600gt has 3.5 times as much memory bandwidth and is a faster cardhttp://www.gpureview.com/show_cards.php?card1=513&card2=525
That might be enough to make a difference in the game.
The fact that it's crashing at a point when it's trying to load a lot of data (more than earlier in the game) makes me think it's either a matter of drivers or not enough resources or a combination of both.
So I still think the problem is the video card.