You are always best to open the system to ensure you have the required port for a video card. Most times this will be PCI Express(check under System Devices).
The reason I say to open it is that I have seen some cheaper systems back in the day that had the spot for a card, but the slot was not installed. To add to this the board will have other pci-e slots used for other devices. So looking is ALWAYS the way to go.