Yeah, OpenGL on AMD is terrible. That probably is the cause.

Its not that terrible his card can run quake 3 at over 1,000fps

OGL extensions limit?
As the example if I run Star Trek Voyager: Elite Force on my HD3850 Agp - most OGL extensions aren't used because the list is trimmed before them. And I got 15-17 FPS.

Starsiege and Starsiegie: Tribes run fine for me (HD 5770).

I get no differences running with or without a GL Extensions Limit in place. The only thing that makes a serious difference is if the rendering of terrain is turned off, i.e. while inside of a InteriorShape that has a partition that would trigger such culling. Since Dynamix never really did OpenGL properly and the DarkStar engine itself uses a really old 1.x subset I tried using a glide wrapper instead but, even with nGlide I get no performance gains. With nGlide I actually get framerates as low as 5 to 1 FPS if I'm in the view of too many unique textures at once. (Is this VRAM thrashing...?)

I'm not really sure what to think here, other than the engine has incredibly inefficient draw calls. I don't get these problems on any other game from the late 90's...

it's more due to Darkstar's lightmap uploads when a dlight gets fired on the terrain. They have a lowres lightmap all over the terrain, and when a dynamic light's gonna be placed they have to take a chunk, do a dirty upsample, and then render a higher res lightmap on top of the chunk and upload it and somehow they've done this in a horrendously slow way through their OpenGL driver (probably an entire new texture allocated and uploaded in RGB instead of a partial update through BGRA). This was slow on nVidia cards at the time too, and is not necessarily "ati opengl suck".

Is a Glide wrapper an option for you? That should be a little better since Darkstar has a much better implementation for Glide than GL. (this does not imply Glide is better than OpenGL as a whole - Dynamix biffed it then, and most ICDs were too premature to improve it with.)

Well I tried nGlide like I said, but when I'm in the vicinity of complex .dis shapes with alot of unique textures the framerate drops to 5 FPS. Not sure what to think there.

The terrain rendering framerate doesn't seem to change.