I have one PCI x 16 slot with 2 DVI-I video card, and 2 PCI x1 slots and 1 PCI v5 slot. I cannot find a video card that will run in a Windows7 computer for the third monitor that isn't stupid expensive so I want to know if I can run the third monitor using a USB to VGA adapter or do all my monitors need to be hooked up using the USB to VGA adapters?