How many plugs are there on the card, and what sort? That's a good place to start, obviously...
If your card can't do it, and you have room for more PCI slots, then you can get a PCI video card, and just have two in there. That's what I have done with my G3; the second card is a cheapo ATI bottom-of-the-line card from a couple of years ago. I don't use it for 3D games or heavy graphics work or anything, so it's fine for me.
What is the robbing of a bank compared to the founding of a bank?
-- Bertold Brecht