Based on my understanding of unified drivers, their setup file includes all of the supported cards' drivers, but when you start the installation it detects your specific video card and installs the appropriate drivers for it, meaning it doesn't install the drivers for all ATI cards (ranging from Radeon DDR through Radeon X800 XT PE), so you'll have to reinstall the drivers when you swap your ATI with an ATI, but maybe cards from the same series (9600 series, 9800 series etc..) don't need driver reinstallation, and there's also the possibility that Phoenix mentioned.