What laptop do you have? Linux does not support Optimus natively; If you would like to utilize both graphic cards, check out the bumblebee project. Please note that bumblebee is not official, and using backtrack, you will most likely run into quite a few problems. Besides the warning, here is the link for you - https://github.com/Bumblebee-Project/Bumblebee
Also, read my one thread about how I got bumblebee working on my Alienware M14x, under Fedora 15.