I`ve checked the specs on Radeon x600 series, and I found that it was released in 2007, and only supports Shaders v2, and overall a really old card - well it used to be great for gaming in 2007.
This would explain why it doesn`t want to run the game... but can you confirm the video card is indeed that old and doesn`t support Shaders v 3?
Any Radeon new HD cards (or even going back to 2008) should run DoF just fine - as long as they support Shaders v3.
SOURCE:
http://uk.ts.fujitsu.com/rl/services...radeonX600.pdf