As has been said in the openGL newsgroups), if you have more than 1 card, then the only way you can *accelerate* ALL screens is to have the VENDOR support this. MS doesn''t, since they want people to use DX. MS hasn''t updated the core opengl32.dll for a long time, and they will never update it besides the basic stuff.
So the hack is that the vendor must do all the work, and MS could care less. I guess being a monoply doesn''t help the matter any either.
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Note, I think it was 3dLabs (or one of the other higher end gfx guys) that provides custom drivers to do this, and I think nvidia was working on it...