Three monitors

I have a Sapphire Radeon HD 4870 graphics card and use two monitors. Though I'm happy with my setup now I might want to try three monitors in the future, so I was curious as to what I would need to do that.

My current graphics card has only two DVI outputs, so I can't connect three straight to it. Are there cables that allow one DVI output to go to two monitors, and still be able to split them as a shared desktop? Another alternative I see is to get a second video card. Not XFire--I know that then only the outputs on the main card will work. But if I were to take, say, a Radeon 3650 and install it as a second video device would I be able to use that to attach another monitor or two? Would there be any possibility of driver conflicts? Another possibility is that I have an old BFG 9500GT lying about. I doubt ATI and Nvidia would mix well, but would it be possible to use that?

I'm just curious about this is all.

Intel Pentium Dual Core E2200 2.2GHz OC@2.86GHz
Asus P5Q Pro
OCZ Platinum 4GB DDR2 1066
Sapphire Radeon HD 4870 1GB
Corsair tx750w

I you want to add a 3rd or 4th monitor then yes you will need another video card. There is no reason you can't just pop in that 9500 GT and off you go once you install the drivers, but I would suggest trying to pick up a video card of the same generation as you are using now, so any 4000 series ATI card would be your best route. Even a cheap HD 4350 such as this would be a good option. This particular model is one of the few models with dual dvi, most offer DVI, HDMI, and VGA - those models are cheaper and if you dont mind using some adapters you can do the same job as the above card.

The problem with using an ATI card with an Nvidia card, or using a modern ATI card with an old ATI card is simply drivers and whether or not you will run into conflicts with those drivers. More often than not most people dont have any problems what so ever, but when problems do arise it is a pain in the neck to trouble shoot and often times its just a smarter move to buy a new low end card instead of using an old one.

Thanks mate. I think I'll try the 9500GT first. Turns out I have an old CRT monitor in the basement and it works, so if the 9500GT will work then all I need to buy is a DVI-VGA converter and I'm set. If that doesn't work I'll see what I can pick up for cheap in the way of 4000 series video cards. Thanks again.