Your new Matrox 3d card is actually a video card. Uninstall the drivers for your PCI-card, turn off your computer, unplugg power, remove your old PCI-card, insert your matrox-card unto your mother-board, plug in your monitor to your matrox-card (there are usually two ports, trial and error to see which one's the right one), plug in power and start your computer.
Now your OS will (hopefully) detect your new hardware, follow installation procedures from your matrox manual.