I have two 22″ monitors hooked up to my computer through DVI. But the other day I wanted to try out if it would work with three monitors too. However, my ATI/AMD PowerColor 4870 graphic card has only two DVI video outputs, so I borrowed my brother’s video card, which is an ATI 3650. After plugging it in to a PCI-E bus, I realised that it hasn’t even a Crossfire connector. I did some searching and found out that a Crossfire bridge is only needed when you want to take advantage of the extra video card in games and such, which I wasn’t interested of. Then I hooked up my brother’s 17″ monitor to the 3650 card. The monitor had only a VGA input tho, while the card only had DVI outputs, so I had to use a DVI-to-VGA adapter.
I started with booting up Windows 7, and it worked fine with 3 monitors. However, I didn’t test it for too long. Then I rebooted the computer and started up Ubuntu 10.10 instead, to see if it would work. I had to do some configurations in the ATI Catalyst Control Center, but then it worked there too. However, it worked a bit strangely, almost like its own desktop. The 17″ monitor had the standard panel configuration for a single monitor, and I wasn’t able to drag windows between it and the other two monitors. I didn’t have much time tho, and my brother wanted his card and monitor back, so I never solved that odd problem. Maybe I had to adjust something in CCC, or somewhere else, I don’t know.
To summarize this post: You can use three monitors by plugging in a second (AMD/ATI) graphic card. The card must not be of the same model, or even of the same generation (ATI 4870 and ATI 3650). You don’t need a crossfire bridge. Though, I can’t say if this applies on Nvidia cards too.