Since I've got no idea about what you UI looks like, I can only advice you to organize you UI in a manner that supports various screen sizes – but you have probably reached that conclusion yourself.
You can use something like:
AvalonDock on Codeplex/[
^] to achieve this quite easily.
Another approach is to scale contents using something similar to this approach:
UI Scaling (UI Zooming) with WPF[
^]
Regards
Espen Harlinn