Dual Quad-Head video card setup - NVS 400

HP dc7900 shows two PCI-e x16 slots - check!
Make sure your NVS 400 cards are PCI-e x4, x8, or x16 models to be slot compatible with those two slots.
Make sure your monitors use the same video connections as the NVS 400 cards you select (likely DVI, as opposed to HDMI or VGA.. although with adapters you could likely resolve those issues, but avoid the drama).
Make sure your monitors fall within the resolution spec of the NVS 400 cards (likely not a problem, but they do top out at 2048x1536 (typically), some large monitors may exceed this resolution.
Make sure your OS supports 4 monitors (should be fine with XP or Vista).

Otherwise, you should be in pretty good shape.  If you opt for more powerful video cards, you'll need to make sure you have adequate power supply and the likely PCI-e power dongles required to power them.  I don't think most NVS 400 series cards require power outside the PCI-e x16 slot power.

Looks like you've done your homework.  You probably want to study up a bit on the Nvidia drivers for those cards and enabling quad monitor (and perhaps most importantly, arranging the monitors logically to match the physical layout for easier mousing/etc).  

Send me good info on shorting stocks. :)

Doh, I cannot count today.  8. XP supports up to 8, check.

Each NVS400 says it can support 4 monitors, looks like they use dual-dvi dongles on each port, so match that to monitors.

If you go with a newer NVS450 series, you can get support for 2560x1600 on a single displayport (instead of DVI, which is typically limited to more like 1920x1200 without dual link).

Here is a related question already answered here:
https://www.experts-exchange.com/questions/23782046/8-Monitor-Setup-Streching-an-application-over-all-the-monitors.html

TechnoButt thanks for the response.

Unfortunately I am not into that type of trade, this is for a digital signage proof of concept using 6 32" Sansung LCD's at 1360x768. Although the LCD panels themselves are large, I am thinking 1360x768 taxes the card the same for a 19" and a 40" granted that is what both panels are set to.

And you are right, which I will reward after your next response, after I posted the question I ran across the sku for the 450 and it is actually cheaper than a 440 or 400 for me. Great recommendation.

So now you know the rest of the story do you see anything wrong with the dc7900 and two NVS 450 x16 cards to achieve 6 lit panels?

Regards,
Ron

Thanks for your responses they are helpful.