I used to run 3 22" on my main. I just had to have a second video card. Now in my setup, I have an SLI board, and I just had 2 PCIe cards, non SLI with 2 LCD's hooked to one, and the final LCD hooked into the second card. That setup also allowed me to use a program called "SoftTH" to get 5040x1050 resolution in games if you wanted.

And with SoftTH, you can run different resolution monitors.

Here's a vid of my brother's setup, the same way, but with 1 30" and 2 20":
http://www.youtube.com/watch?v=G5pWnSkfszg