Found some information about the problem

Found on dejanews or google

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> Hi, I have a windows openGL application that uses texture maps. On a
> system with an Nvidia geForce 2, all is well. However, on my ATI
> Radeon 9000 system, the textures look as if they are being stored in
> something like 4 bits per channel colour. (The images I send to the
> card are 24 bits per pixel).

Are you using GL_RGBA8 or GL_RGBA for your internal format in
glTexImage2D()? Using GL_RGBA8 will likely give better results on an ATI.

> If I change the Texture preference slider on the openGL tab in the
> display settings from "quality" to "high quality", this fixes things.
> My question is, is there a way of setting the card to "high quality"
> texture mode from software. Perhaps an opengl extension command?
>
> Many thanks for any help
>
> Matt Taylor

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and here

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http://www.flipcode.com/cworks/issue05.shtml