It can simply be that your graphics card just don't work well with brink since that's what they're most famous of, like 30% of all video cards can't start brink due to incopability and like 30% can't run it well. (Of the ones that are supposed to be able to run Brink)
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I'm not home atm, but when i do get home i'll post a link :)
EDIT : Brinkkit