I have a M4800 and have 3 monitors running windows7. I have connected 1 monitor to the VGA port, 1 monitor connected via usb video adapter and i have 1 monitor connected to display port. the one on the display port is not getting extended display. do i need another video card or Do i have a misconfiguration?
This may depend on the configuration you have. I think there are several options on that model. But from my quick look, it appears as though 3 external monitors is no problem, at least to the version that has the high res internal screen.
See here as a reference.