I couldn't find the answer to this question on any forums so I tried it myself.
Installed a Palit Nvidia GeForce GTS 450 video card.
Set video BIOS to make external card the primary video card.
Once in Windows 7 I had to install the Intel HD graphics drivers to get the third display to show.
Running two displays from Nvidia card (hdmi and dvi-i) and one from onboard video (dvi-i).
I then connected another monitor to the onboard video and had a total of 4 monitors running.
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