To the original poster...
I'm guessing your on a Macbook Pro. Cause this two video card approach is exactly how they are setup.
So to answer your question and give you a hint to what your going to encounter next ..
1) you dont have to do anything .. as soon as you init your display using OpenGL it will switch to the dedicated card. There is a GLX util you can download that monitors the cards and will show you it autoswitches.
2) now the next challenge.. which version of opengl do you want to use? By default the dedicated card will be a opengl 2.2 profile. If you want the opengl 4.1 profile you will have to specifically init the opengl profile asking for ... 3.2 CORE ... (yes 3.2 CORE = 4.1 implementation.. if you ask for 4.1 you will get an error.. welcome to the nuances that is Mac gaming