opengl 1.2 for ATI Radeon X850

My graphics card is ATI Radeon X850. I have installed the driver package. And I got opengl 2.1 when I used glGetString(). But my header gl.h is still the old one. I need to use 3D texture, but the GL_TEXTURE_3D is not defined there. Do I need a different header for opengl 1.2 or higher version? If so, where can I get it?
Thank you.

Go to :

you need glATI.h