Your video card being built in DOES mean that its not replacable, but your motherboard is equipped to accept alternate video , using the PCI slot.
* * * http://www.directron.com/howtovideo.html * * *
All you do is take the card, and stick it in the white PCI slot on your motherboard. screw it in, plug up your monitor and its ready to go. All youll have to do is go to the website and download and install the newest drivers for it.
You may have to disable the onboard graphics card in the bios, or thru windows first tho. In windows you just go to the device manager, and look for "display adapters" then disable it from there. then you shut down the computer, install the video card, and when you reboot, windows will automaticly detect the new video card.
Its very simple.
[edit]
Also, when choosing a video card , id reccomend Nvidia. Good solid card, and the drivers and user interface is easy to use.