I am sure it is very possible. If you wanna play two games at the same time, or play a game and watch a movie in HD or something. I am not sure what you would really need it for.
It would also be useful to have a dual core or fast processor to be able to perform tasks with reasonable speeds on both screens.
Its easy, plug them both in, turn on your comp, install all the drivers for each card. Right click on your desktop>>properties>>settings. Right click on the second monitor and activate it.