OpenGL - DirectX?

Im not exactly the best when it comes to hardware drivers .etc, but I use DirectX to play my games, as WinXP set it up as default. But for some game modifications I need OpenGL, whats the difference? and how do I setup my computer with OpenGL drivers when DirectX is already there? (running nVidia Geforce 2 MX 400, which is compatible).

anyone?

I know that this is porbably a dumb question, but i need the answer .

anyone? its really easy, and yet i need it desperatly .

OpenGL support is integrated in the display driver but you have to use the driver from the manufacturer not the driver that installs with XP.

Grab the latest DetonatorXP driver from www.nvidia.com and you should be set.