If it is mostly stuff like "Window Positions" (wich is minor) or Connection Strings (wich rarely changed), the User and Application settings are a good place to look too:
http://msdn.microsoft.com/en-us/library/bb397750.aspx
They are stored someplaces that make sense in XML format, but overall you do not need to worry where they are saved - they just are.
When picking a place to store information it is important to remmember that you are never guaranteed to have writeaccess to the programm folder (since XP) and that the Paths to User AppData and All Users AppData might change, so always ask windows where
they are.
Let's talk about MVVM: http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/b1a8bf14-4acd-4d77-9df8-bdb95b02dbe2 Please mark post as helpfull and answers respectively.