Question concerning a video card

[jjvacc]

I have a dell inspiron 530 desktop. How I used to have a dual port video card thus giving me the dual monitor ability. However, this computer's video card is build right on the motherboard. Now I had an extra dual port video PCI card that I tried putting in the machine, giving it a total of three monitor plug-ins. I plugged a monitor into both the ports on the card, which yielded the same picture on both screens, then I tried plugging one of the monitors into the port on the motherboard, which did not work (the monitor had no picture on it). Is there anyway I can have dual monitors with this type of computer? If I buy a single port video PCI card will that work?

Thanks in advance,
John