Is there any way to create a Silverlight "Out of Browser" Application that can have two windows each on it's own screen and have these two windows communicate?
Apparently in Silverlight 4 you can "Control over aspects of UI include window settings such as start position, size and chrome" so automatically placing the windows on each screen shouldn't be that big of a deal... the main issue is communication.
Judging from this tumbleweed question and a few other forum hits, it's not possible to set the window size programmatically in Silverlight 3.
You could "cheat" by docking a splitter into your window and having the user size it to the full size of both monitors manually, and slide the splitter bar to the "seam" between the monitors. Not the best solution but it's probably the only option for dual-monitor support for now.