the instructions that come with any card should be sufficient enough to help you install it on your own. it is fairly simple. you will need to power off the comp, of course, and open up the case itself. hook up the card, install the drivers and disable the old onboard drivers and you should be good to go. your games will look a lot better and play smoother, as will movies, pics, they will all display faster and better quality.
Edit: having a graphics card will also free up that shared memory and give it back to your programs.