Only the new 180 version beta drivers support multiple monitors. (in SLI)
I have heard they are somewhat buggy though, and it doesn't always work exactly as it should, and you take a performance hit.
If you want to run 3 monitors, you have to have an addtional GPU outside of your SLI'd cards. Go here and read this.....http://www.hardwarezone.com/articles/view.php?id=2728&cid=3&pg=3