Multiple Monitor Setup

I plan to purchase two dual monitor desk mounts, 4 LCD monitors to mount of them, and either a new, or additional graphics card if required. I've been out of the loop for a awhile and need assistance choosing appropriate hardware.

I've already decided on the mount linked below since I can't use desk clamp or wall mounts.
http://www.monoprice.com/products...1&format=2 (Click play youtube video under the picture of the mount to see more detail.)

I am looking for 21-23" monitors with 1920x1080 or 1920x1200 resolution that have a very thin edge on all sides of the display. Price per monitor sub $240. Depth is not important, but weight is (tempered glass desk). I am not sure which display input type is appropriate.
Currently I have an Asus P5E motherboard which has 1 free pci-express x16 slot, and 1 free pci-express x1 slot. The other PCI express x16 slot has an Nvidia GeForce GTX275, with dual DVI/HDMI(via adapter).

From a previous PC, I have an ATI 3870 with dual DVI/HDMI(via adapter). I am hoping it is possible to simply plug in the ATI card and use it for the additional 2 monitors, but still use the GTX275's horsepower for games (or both card's horsepower)? If not than what additional graphic card(s) should I buy? Something with 2 DVI ports would work but it would be nice to have displayport outputs so I can expand to 6 monitors in the future. Also that would mean the monitors would need displayport inputs in addition to DVI. That'd be nice since I could than connect my macbook pro and thinkpad x201.
I am very indecisive on the graphics card options, assuming the ATI card will not work. I'm sure additional research on my part will be required. There is probably hardware on the market I'm not even aware of.

Anybody have suggestions on lightweight and thin-edged monitors? Perhaps an inexpensive additional graphics card that support 2 to 4 additional monitors?

Actually, try to plug in both the gpu's and try if all monitors work. I thought you would need sli but you don't, never thought gpu's could work together without sli/crossfire

In SLI you can use 2 monitors max.
Non SLI you can use 4 monitors. Cards can be different but must either both ATI or both Nvidia.
If you are running Windows 7 and have Lucid Hydra you can mix ATI and Nvidia.
For 6 monitors you need a ATI Eyefinity card, like ATI Radeon™ HD 5870 Eyefinity 6 Edition Graphics.
You are looking at $400.00. You need 600 Watt or greater power supply with one 75W 6-pin PCI Express power connector and one 150W 8-pin PCI Express power connector recommended.
I recommend Eyefinity, if you want to go for several monitors.