I have a PC (Dell Optiplex 740) with a ATI HD 4300/4500 in it. It has 1 x DVI, 1 x VGA and 1 x HDMI outputs on it. I run windows XP. Why is it that I can only run 2 of the 3 outputs at once when the card has 3 on it??? Is it possible to run three outputs without buying a second card?
You need a Radeon video card with Eyefinity function to be able to support 3 monitors. Most Radeon HD 5xxx series and HD 6xxx series support this feature, budget card may exclude it.
Additionally, Eyefinity does not work with Windows XP. Therefore you would need to upgrade to Win Vista or Win 7.
Your cheapest solution is to buy a 2nd video card with a PCI interface and have the 3rd monitor connected to it. That's PCI not PCI-e which is a newer interface and is not compatible with the old PCI interface from the early 1990's.