Can you use the asp.net membership provider in a windows application?
Yes. Membership, roles and profiles are all features of Visual Studio 2008 Client Application Services (Services tab of a project properties)
http://msdn.microsoft.com/en-us/library/bb384297.aspx
http://channel9.msdn.com/posts/DanielMoth/Client-Application-Services-with-Visual-Studio-2008/
I have a winform app that talks to DotNetNuke (DNN). DNN uses the Asp.net membership provider, so the source will work for other apps that use that membership provider as well. It's a very simple app, so you should be able to read the source easily.
http://www.datakido.com/downloads/Token/ViewInfo/ItemId/3
You should be able to adapt the source to work with WPF.
Yes, you can.
All the configuration can be done within app.config instead web.config of asp.net.