Yes, it is possible to have two GPUs running two seperate displays. The OS (XP vs Vista) is a big deciding factor in if two different drivers can be installed. If you have Vista, you'll need another card that uses the same driver - 8800 GT + 8400, 8500, etc
If you have XP, there is a work-around for installing an nVidia and an ATI driver
Mmm... Seems a good option (since I got XP), but a difficult one. Do you have any idea where can I find detailed instructions to do that.
By the way, I'm also concerned about the noise and heat issues with the 4850, so that's another factor for not buying it