Direct 3D is faster then OpenGL on my TNT2? I've always been lead that OpenGL was better, and since nVidia is supposed to be the best in the OpenGL department, I don't see how it could be so SLOW!?
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Ok, I had the very same problem as you Sven.

So, try downloading the latest VIA 4-in-1 package at their site:
http://www.via.com.tw/drivers/index.htm

When you install it, install the AGP...