[all variants] Dual monitors, where to begin?

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http://ubuntuforums.org – I'd like to configure my PC to run two monitors. I've never done this before so it took me a while to understand my computer only has one graphics card. After reading up apparently it's possible to hook a second graphics card instead of trashing the original card for one with a dual output. After looking around I can't really find if this is possible for me in particular, though. "Graphics Gallium 0.4 on ATI RV370" tells me I have an ATI RV370. So then by the previous logic I would assume I can buy another ATI RV370 and hook it up. Am I wrong, or am I right? And if I am right, how (Hardware)