If your video card is integrated, that means it's a part of your motherboard. I believe you would have to get a new motherboard altogether to have it work with a video card that isn't integrated. Also, if your computer is old, let's say, before 2005, you would probably also need a new processing unit, as new motherboards aren't compatible with old processing units.
For shame. You might as well buy an empty computer tower, buy the parts and build a new computer. If you buy the parts separately, it's almost always more worth it than a pre-built one. Same money, double the specs.