Hi Tonkadad: DVI is digital, and is supposed to have a better quality video image. All my 8400 GS cards have 1 VGA out and 1 DVI out. I use DVI cables whenever I can (provided that the monitor has a DVI in, and the DVI cable is long enough). The rest, VGA (either from the VGA port out from the video card, or DVI port out from the video card via a DVI-VGA adapter). For the life of me, I couldn't tell them apart and I have many monitors side by side and I stare at them all day long. I think for practical purposes, and especially with trading - simple primary colors, 2D line charts... it really doesn't make much difference.
Each video card needs the driver software from the manufacturer (e.g. Nvidia). Windows OS will go through the driver to manage the monitor position and display images across screens. No a problem.
I am glad that you got that that configuration. I think it depends on the motherboard - computer manufacturer. For many that I purchased, even though the motherboard supports dual monitors (Intel HD graphics chip onboard the MoBo)... as soon as I plug in an external video card in one of the PCIe X16 slots, the HD graphics output is immediately disabled.
I used to have Dell 1905 Ultrasharps... VGA and DVI seemed identical. With other monitors, however, significant difference. Wouldn't use VGA unless had no other choice.
Let's not forget to tell him, though mixing video cards may or may not work, "it's better that all video cards are the same"...
I knew it was a ways back. I was trying to recall the OS on my first 4-monitor rig. (At the time, the only apparent choices for 4-monitors seemed to be 4x single head cards or a Matrox quad. Of course, the Matrox was more than double the cost of the 4 single heads.) I chose the 4x singles... ATI Xpert... I believe they had only 2MB of VRAM.
Yeah. That's a great advice. I do have a mix of PNY 8400 GS versus EVGA 8400 GS on the same box. They worked together okay. The driver is provided by NVidia just the same. I also have cards PNY 8500GT and PNY 8400 GS side by side. They worked together okay. (But they are within the same 8000 series family though.) Mixing video cards from different manufacturers should be avoided.