Couple of things you will need.
Recent ATI Card (6870, 6950, 6970 is reccomended or better e.g. Crossfire)
You need 3 monitors ALL be able to display the same resolution. (e.g. 1920*1080)
you will also need at least 1 connected via Display port.
so either make sure you have atleast 1 native display port monitor or use one of the following adapters (depending the outputs on the card)http://www.newegg.com/Product/Product.aspx?Item=N82E16814999034
then its just a matter of enabling the function in the driver software.