No current application of multi-gpu can support multi monitor setups. But matrox has a device called Head2Go. it basically makes your screen size (max capacity that is) 1280*3 x 1024. Head on over to http://www.widescreengamingforum.com/wiki/index.php?title=Main_Page they have alot of information on that kind of stuff. Personally im waiting for the ability to run 3 2405's in a TripleHeadToGo configuration.
Edit: Make sure to read all up on the specifications of matrox's TripleHeadToGo. They're limitations that will have an impact currently on what hardware your're running.