This article best covers this:
http://www.pcworld.com/article/216667/Connect_a_Third_Monitor_to_Your_PC.htmlAlthough as far as S-Video goes, I have only experienced it disabling or cloning the secondary display port on a dual-display adapter. And only way to get a 3rd to work was by cloning one display with another say the DVI with S-Video cloned and VGA extending to the DVI for extended desktop, but the DVI and S-Video displaying the same display not a actual 3rd extended for one teamed desktop across 3 displays with that much desktop space etc.
Video cards with HDMI on the other hand allows this to be done
on some video cards, but not all!
Best way to get 3 working is 2 video cards using 3 of the 4 ports. Some cards will allow for this, others will fight you along the way, and some will not work along side others. The USB Video Adapter option is one way to get a 3rd, BUT quality of this display will only be good for word documents and power point presentations, also I have heard complaints of the USB Video Adapters being blurry and not very sharp with pictures etc.
Also about 6 years ago I installed a GeForce video card into a HP S5000 series Pentium 4 2.8Ghz HT computer with 1GB RAM and when looking at the display properties it showed 3 displays available ( 2 x nVidia + 1 x Intel Integrated Video ). So it appeared that this system allowed for integrated to function along side this nVidia video card. *This may have been because the nVidia video card was a PCI Geforce 6200 instead of a PCIE or AGP type of video card that would disable the integrated video when a PCIE or AGP port is populated. So if you have a older video card of the older PCI type which is dual-video, you can install that and see if the integrated will remain enabled along side the added PCI Video Card. ** Note: Video performance of PCI video cards are very limited. You would not be playing 95% of the games out there on this etc because the PCI bus is a bottleneck for any better performance.
