-= For the record =-
I've finally bought what needed to test it and ..
No .... I could not even clone the display with two video card from two different Brand
In my case it was a nVidia 8400GS and a ATI Diamond PCI 2400Pro.
One last thing need to be tested
DualHead2Go from Matroxhttp://www.matrox.com/graphics/en/products/gxm/dh2go/