I had tried several years ago to attach a third monitor using the onboard video along with the PCI-Express video card. I tried several different configurations but found out this type of solution was not supported. I happened to catch an episode of Defrag on Channel 9 that said it was possible to do with newer systems. So once again I tried to connect a third monitor using the onboard video along with a PCI Express Video card. Thankfully it worked this time around. I finally have my third monitor up and running without having to purchase any additional hardware. I have not been able to pinpoint what happened to allow this. If you have bought a computer in the past couple of years it will probably work.
Defrag Show Link:
http://channel9.msdn.com/Shows/The-Defrag-Show/Defrag-WHSMC-Error-1325-Using-Onboard-VGAPCI-Video