Is it possible to install two dual output PCI graphics cards for four total displays?

I have a 5 year old Dell Optiplex GX520 (Pentium 4, 2GB DDR2 RAM) which has two 120-pin PCI card slots (one is currently in use with my nVidia GeForce 8400GS dual output (DVI & VGA) graphics card) and one 36-pin PCI Express slot. I need to add a 3rd or 4th 17” monitor to my desktop and wondering the best way to achieve this. Is it possible to install a second PCI graphics card?