OpenGL, Ati FireGL and 3ds Max

I need some information about the OpenGL library.
I installed the video driver (Ati FireGL V3600 256mb), 3ds Max and then the Ati Maximum driver for 3ds Max based on OpenGL 2.0.
This driver improves the rendering preview. What does it mean effectly? Which the real difference between standard OpenGL and the Maximum Driver?

If I use FireGL standard driver, I am unable to use OpenGL (I see a strange pattern in every viewport when I start softwares such as 3ds, Rhino, Adobe Photoshop extended). With the Maximum driver I can use OpenGL with 3ds, but if I install Autocad, both the softwares stop to work. Why?

Which is the real difference between OpenGL and DirectX with 3ds?
Does OpenGL 3.0 work under XP Pro 32bit?
Thank-you very much for your answers.