You are doing the right thing by using a graphics card over the built-in controller on the motherboard. You should notice an overall speed up of your computer (though it may not be that much). I'm assuming that the card you got came with instructions, if not, here is a general way to install a graphics card.
1. Install the drivers for the card (without the card in the computer yet)
2. Turn off computer and install card
3. Plug monitor into card and turn on the computer
4. If you can see and use Windows, it worked! If not, plug your monitor into the orignal card, go to Display Properties, then Settings, open the pull-down menu and select your new card. Hit Apply. The screen should go black. You now have about ten seconds to plug the monitor into the new card and hit okay in the confirmation box. If you don't do this, the computer will switch back to the old graphics card.
You can safely disable the Intel card once you've made sure your new card is working.
Hope this helps! :grinthumb