You can have both cards under Windows 7 without problems. Each control panel will function and in many cases you can change the desktop resolution of the other card from each others control panel as well.
I have two AMD cards in now, each with four displays. I want to add another 4 and already have a Nvidea Quatro which only takes up a single PCIe slot ( since I only have one slot left). I could buy a AMD but the single slot cards with 4 outputs are expensive so I figured I would use what I have.