Because odds are that you dont have the OpenGL driver for that card working.

How to get 3d working? Buy an nvidia card. If you want more detail check the linux driver forum on rage3d.com. Youll never buy ATI again after about 5 min of lurking through those threads.

Theyre supposed to release a driver that works with the current version of x.org and amd-64 processors in january. Supposedly the drivers are already finished but they cant release them because the people in charge of their web servers are all on vacation. In other news, some people still believe OJ is innocent.

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In order to see if you have opengl acceleration working type glxgears in console and let it run for a while. If youre only getting 300-400 FPS then youre running without hardware acceleration. With it you should be in the thousands.