So you want a GPU working on each display? You do NOT want SLi then, just making sure.
What you need is to find a board with four PCI-e X16 slots.... The Gigabyte GA-8N-SLI Quad Royal is one of them. Sckt 775, though. You plug in four cards, no SLi bridges, do NOT enable SLi in the OS or BIOS, plug a monitor into each card. Should work..
I checked on the BIOS updates, it might work with Core 2 Duo, inquire with Gigabyte before hand.