Popup control outside of Silverlight application

It is not possible to have a popup beyond the boundaries of the Silverlight application container.

However, you can popup a HTML div positioned where you want it and launch a second Silverlight in that div. Alternatively, you can open a new window and insert the second Silverlight app in that div.

More importantly, you can get the 2 Silverlight applications to communicate with each other using Javascript or inbuilt Silverlight communication channels (only available from Silverlight 3).